This page has only limited features, please log in for full access.

Dr. Douglas Smith
Department of Mechanical Engineering, Baylor University, Waco, TX 76798-7356, USA

Basic Info

Basic Info is private.

Research Keywords & Expertise

0 Additive Manufacturing
0 Polymer Composites
0 topology optimization
0 Finite elements
0 Design sensitivity analysis

Fingerprints

Additive Manufacturing
Polymer Composites
topology optimization

Honors and Awards

The user has no records in this section


Career Timeline

The user has no records in this section.


Short Biography

The user biography is not available.
Following
Followers
Co Authors
The list of users this user is following is empty.
Following: 0 users

Feed

Journal article
Published: 31 July 2021 in Additive Manufacturing
Reads 0
Downloads 0

Fused Filament Fabrication (FFF) is a widely used Additive Manufacturing technology with a growing user base. Unfortunately, users of FFF have limited resources for easily and cost-efficiently characterizing the materials from the ever-expanding polymer filament market. To address this issue, we constructed a low-cost device and measuring procedure based on the pressure drop in the polymer melt flow through an FFF nozzle which is used to compute the filament material rheological properties. In this approach, an analytical pressure drop model based on the Generalized-Newtonian-Fluid power-law model is employed where the consistency and power-law indices are determined from the measured pressure drop and volumetric flow rate through a nonlinear regression curve fit. The applicability of our device was demonstrated with six commercially available FFF filaments (four unfilled polymers and two carbon fiber polymer composites) by comparing the predicted viscosity model parameters to those obtained from measurements using a commercial rotational rheometer. A Filament Flow Index (FFI) capable of characterizing the flow of melted filament similar to Melt Flow Index is also proposed to assess the extrusion of materials used in FFF part fabrication.

ACS Style

Jingdong Chen; Douglas E. Smith. Filament rheological characterization for fused filament fabrication additive manufacturing: A low-cost approach. Additive Manufacturing 2021, 47, 102208 .

AMA Style

Jingdong Chen, Douglas E. Smith. Filament rheological characterization for fused filament fabrication additive manufacturing: A low-cost approach. Additive Manufacturing. 2021; 47 ():102208.

Chicago/Turabian Style

Jingdong Chen; Douglas E. Smith. 2021. "Filament rheological characterization for fused filament fabrication additive manufacturing: A low-cost approach." Additive Manufacturing 47, no. : 102208.

Journal article
Published: 16 May 2021 in Materials
Reads 0
Downloads 0

Numerical studies for polymer composites deposition additive manufacturing have provided significant insight promoting the rapid development of the technology. However, little of existing literature addresses the complex yet important polymer composite melt flow–fiber orientation coupling during deposition. This paper explores the effect of flow–fiber interaction for polymer deposition of 13 wt.% Carbon Fiber filled Acrylonitrile Butadiene Styrene (CF/ABS) composites through a finite-element-based numerical approach. The molten composite flow in the extrusion die plus a strand of the deposited bead contacting the deposition substrate is modelled using a 2D isothermal and incompressible Newtonian planar flow model, where the material deposition rate is ~110 mm/s simulating a large scale additive manufacturing process. The Folgar–Tucker model associated with the Advani–Tucker orientation tensor approach is adopted for the evaluation of the fiber orientation state, where the orthotropic fitted closure is applied. By comparing the computed results between the uncoupled and fully coupled solutions, it is found that the flow-orientation effects are mostly seen in the nozzle convergence zone and the extrusion-deposition transition zone of the flow domain. Further, the fully coupled fiber orientation solution is highly sensitive to the choice of the fiber–fiber interaction coefficient CI, e.g., assigning CI as 0.01 and 0.001 results in a 23% partial relative difference in the predicted elastic modulus along deposition direction. In addition, Structural properties of deposited CF/ABS beads based on our predicted fiber orientation results show favorable agreements with related experimental studies.

ACS Style

Zhaogui Wang; Douglas Smith. A Fully Coupled Simulation of Planar Deposition Flow and Fiber Orientation in Polymer Composites Additive Manufacturing. Materials 2021, 14, 2596 .

AMA Style

Zhaogui Wang, Douglas Smith. A Fully Coupled Simulation of Planar Deposition Flow and Fiber Orientation in Polymer Composites Additive Manufacturing. Materials. 2021; 14 (10):2596.

Chicago/Turabian Style

Zhaogui Wang; Douglas Smith. 2021. "A Fully Coupled Simulation of Planar Deposition Flow and Fiber Orientation in Polymer Composites Additive Manufacturing." Materials 14, no. 10: 2596.

Journal article
Published: 29 April 2021 in Additive Manufacturing
Reads 0
Downloads 0

Assessing the material stiffness of fiber reinforced polymer composites deposited in Large Area Additive Manufacturing (LAAM) is needed to define the process-structure-property mapping for the LAAM technology. While the screw-extrusion-based LAAM systems yield a distribution of fiber aspect ratio (i.e., length to diameter ratio for cylindrical inclusions) within deposited beads, most composite micromechanical models ignore the fiber geometry variation and instead assume a single value of fiber aspect ratio. This paper presents a statistics-based homogenization approach for including the fiber aspect ratio distribution in the prediction of the elastic properties of an extruded polymer composite bead. The fiber length distribution of a 13 wt.% Carbon Fiber reinforced Acrylonitrile Butadiene Styrene (CF-ABS) processed through a LAAM deposition system is measured using high resolution optical microscopy. The Weibull probability distribution function is employed to statistically describe the measured values. The fitted probability density function is then incorporated into a fiber orientation homogenization approach to compute the variability of the elastic properties of the extruded composite. Elastic properties predicted by our proposed method are shown to differ from those presented in prior studies that ignored fiber length variability. The fiber aspect ratio reduction from fiber length attrition during the LAAM single screw-extrusion is shown to decrease the predicted flow-direction effective elastic modulus by 7%. Elastic moduli computed using our measured fiber aspect ratio distribution and proposed homogenization approach compare well to reported data from previously associated experimental studies.

ACS Style

Zhaogui Wang; Douglas E. Smith; David A. Jack. A Statistical Homogenization Approach for Incorporating Fiber Aspect Ratio Distribution in Large Area Polymer Composite Deposition Additive Manufacturing Property Predictions. Additive Manufacturing 2021, 102006 .

AMA Style

Zhaogui Wang, Douglas E. Smith, David A. Jack. A Statistical Homogenization Approach for Incorporating Fiber Aspect Ratio Distribution in Large Area Polymer Composite Deposition Additive Manufacturing Property Predictions. Additive Manufacturing. 2021; ():102006.

Chicago/Turabian Style

Zhaogui Wang; Douglas E. Smith; David A. Jack. 2021. "A Statistical Homogenization Approach for Incorporating Fiber Aspect Ratio Distribution in Large Area Polymer Composite Deposition Additive Manufacturing Property Predictions." Additive Manufacturing , no. : 102006.

Journal article
Published: 26 March 2021 in Composites Part B: Engineering
Reads 0
Downloads 0

This paper presents a Finite Element Method (FEM) based algorithm to simulate the mutually dependent effects between non-Newtonian polymer melt flow and fiber orientation in Polymer Composite Deposition Additive Manufacturing (PCDAM). The computational approach is employed to analyze an axisymmetric flow with a free surface that defines the melt extrudate. The non-Newtonian power law model is applied to quantify the shear thinning rheological behavior of the polymer flow. The fiber orientation state of the composite melt is simulated using the Folgar-Tucker orientation tensor approach, and a streamline-based remeshing technique is applied to predict the die swell of the free extrudate. The non-linear FEM system is solved with the Newton Raphson iteration method. Computed results are compared to those obtained using a flow-fiber one way coupling simulation, where it is shown that the magnitude of flow field along the direction of extrusion, as well as the fiber alignment in the flow direction, both increase when full coupling is used. In addition, the extrudate swell ratio solved by the fully-coupled scheme reduces by roughly a factor of ∼2× as compared to the weakly-coupled flow solution.

ACS Style

Zhaogui Wang; Douglas E. Smith. Finite element modelling of fully-coupled flow/fiber-orientation effects in polymer composite deposition additive manufacturing nozzle-extrudate flow. Composites Part B: Engineering 2021, 219, 108811 .

AMA Style

Zhaogui Wang, Douglas E. Smith. Finite element modelling of fully-coupled flow/fiber-orientation effects in polymer composite deposition additive manufacturing nozzle-extrudate flow. Composites Part B: Engineering. 2021; 219 ():108811.

Chicago/Turabian Style

Zhaogui Wang; Douglas E. Smith. 2021. "Finite element modelling of fully-coupled flow/fiber-orientation effects in polymer composite deposition additive manufacturing nozzle-extrudate flow." Composites Part B: Engineering 219, no. : 108811.

Journal article
Published: 11 September 2019 in Composite Structures
Reads 0
Downloads 0

Micro-mechanics analysis using the Representative Volume Element (RVE) approach implemented with the Finite Element Method has been widely used for computing material properties of unidirectional fibrous polymer matrix composites. However, little attention has been given to viscoelastic RVEs of discontinuous fiber reinforced composites. This paper develops a RVE-based Finite Element algorithm for evaluating the effective viscoelastic creep behaviors of aligned short fiber composites. A parametric study including considerations of fiber volume fraction, fiber aspect ratio and fiber packing geometry is performed through the proposed algorithm. Computed results indicate that increasing the fiber volume fraction decreases the mechanical compliance of the overall compound, and the effect of fiber reinforcements is particularly significant in the direction of fiber alignment. Additionally, increasing the fiber aspect ratio reduces the creep compliance coefficient along the direction of fiber alignment more than coefficients along other directions. The fiber packing geometry affects the values of axial compliance properties at low fiber volume fraction and its impacts become less as the fiber volume fraction increases. We also provide an application to simulate the equivalent viscoelastic creep response out of the RVE approach through ABAQUS user defined material subroutine, and the maximum absolute error between the two sets of data is only 1%.

ACS Style

Zhaogui Wang; Douglas E. Smith. Numerical analysis on viscoelastic creep responses of aligned short fiber reinforced composites. Composite Structures 2019, 229, 111394 .

AMA Style

Zhaogui Wang, Douglas E. Smith. Numerical analysis on viscoelastic creep responses of aligned short fiber reinforced composites. Composite Structures. 2019; 229 ():111394.

Chicago/Turabian Style

Zhaogui Wang; Douglas E. Smith. 2019. "Numerical analysis on viscoelastic creep responses of aligned short fiber reinforced composites." Composite Structures 229, no. : 111394.

Journal article
Published: 01 February 2019 in Fibers
Reads 0
Downloads 0

Mechanical properties of parts produced with polymer deposition additive manufacturing (AM) depend on the print bead direction, particularly when short carbon-fiber reinforcement is added to the polymer feedstock. This offers a unique opportunity in the design of these structures since the AM print path can potentially be defined in a direction that takes advantage of the enhanced stiffness gained in the bead and, therefore, fiber direction. This paper presents a topology optimization approach for continuous fiber angle optimization (CFAO), which computes the best layout and orientation of fiber reinforcement for AM structures. Statically loaded structures are designed for minimum compliance where the adjoint variable method is used to compute design derivatives, and a sensitivity filter is employed to reduce the checkerboard effect. The nature of the layer-by-layer approach in AM is given special consideration in the algorithm presented. Examples are provided to demonstrate the applicability of the method in both two and three dimensions. The solution to our two dimensional problem is then printed with a fused filament fabrication (FFF) desktop printer using the material distribution results and a simple infill method which approximates the optimal fiber angle results using a contour-parallel deposition strategy. Mechanical stiffness testing of the printed parts shows improved results as compared to structures designed without accounting for the direction of the composite structure. Results show that the mechanical properties of the final FFF carbon fiber/polymer composite printed parts are greatly influenced by the print direction, and optimized material orientation tends to align with the imposed force direction to minimize the compliance.

ACS Style

Delin Jiang; Robert Hoglund; Douglas E. Smith. Continuous Fiber Angle Topology Optimization for Polymer Composite Deposition Additive Manufacturing Applications. Fibers 2019, 7, 14 .

AMA Style

Delin Jiang, Robert Hoglund, Douglas E. Smith. Continuous Fiber Angle Topology Optimization for Polymer Composite Deposition Additive Manufacturing Applications. Fibers. 2019; 7 (2):14.

Chicago/Turabian Style

Delin Jiang; Robert Hoglund; Douglas E. Smith. 2019. "Continuous Fiber Angle Topology Optimization for Polymer Composite Deposition Additive Manufacturing Applications." Fibers 7, no. 2: 14.

Journal article
Published: 01 November 2018 in Additive Manufacturing
Reads 0
Downloads 0

The rapid transition of the Fused Filament Fabrication (FFF) Additive Manufacturing (AM) process from small scale prototype models to large scale polymer deposition has been driven, in part, by the addition of short carbon fibers to the polymer feedstock. The addition of short carbon fibers improves both the mechanical and thermal properties of the printed beads. The improvements to the anisotropic mechanical and thermal properties of the polymer feedstock are dependent on the spatially varying orientation of short carbon fibers which is itself a function of the velocity gradients in the flow field throughout the nozzle and in the extrudate during deposition flow. This paper presents a computational approach for simulating the deposition flow that occurs in the Large Area Additive Manufacturing (LAAM) process and the effects on the final short fiber orientation state in the deposited polymer bead and the resulting bead mechanical and thermal properties. The finite element method is used to evaluate Stokes flow for a two-dimensional planar flow field within a Strangpresse Model 19 LAAM polymer deposition nozzle. A shape optimization method is employed to compute the shape of the polymer melt flow free surface below the nozzle exit as the bead is deposited on a moving print platform. Three nozzle configurations are considered in this study. Fiber orientation tensors are calculated throughout the fluid domain using the Folgar-Tucker fiber interaction model. The effective bulk mechanical properties, specifically the longitudinal and transverse moduli, and the coefficient of thermal expansion, are also calculated for the deposited bead based on the spatially varying fiber orientation tensors. Fiber orientation is found to be highly aligned along the deposition direction of the resulting bead and the computed properties through the thickness of the bead are found to be affected by nozzle height during deposition.

ACS Style

Blake P. Heller; Douglas E. Smith; David A. Jack. Planar deposition flow modeling of fiber filled composites in large area additive manufacturing. Additive Manufacturing 2018, 25, 227 -238.

AMA Style

Blake P. Heller, Douglas E. Smith, David A. Jack. Planar deposition flow modeling of fiber filled composites in large area additive manufacturing. Additive Manufacturing. 2018; 25 ():227-238.

Chicago/Turabian Style

Blake P. Heller; Douglas E. Smith; David A. Jack. 2018. "Planar deposition flow modeling of fiber filled composites in large area additive manufacturing." Additive Manufacturing 25, no. : 227-238.

Journal article
Published: 10 April 2018 in Journal of Composites Science
Reads 0
Downloads 0

Recent advances in Fused Filament Fabrication (FFF) include large material deposition rates and the addition of chopped carbon fibers to the filament feedstock. During processing, the flow field within the polymer melt orients the fiber suspension, which is important to quantify as the underlying fiber orientation influences the mechanical and thermal properties. This paper investigates the correlation between processing conditions and the resulting locally varying thermal-structural properties that dictate both the final part performance and part dimensionality. The flow domain includes both the confined and unconfined flow indicative of the extruder nozzle within the FFF deposition process. The resulting orientation is obtained through two different isotropic rotary diffusion models, the model by Folgar and Tucker and that of Wang et al., and a comparison is made to demonstrate the sensitivity of the deposited bead’s spatially varying orientation as well as the final processed part’s thermal-structural performance. The results indicate the sensitivity of the final part behavior is quite sensitive to the choice of the slowness parameter in the Wang et al. model. Results also show the need, albeit less than that of the choice of fiber interaction model, to include the extrudate swell and deposition within the flow domain.

ACS Style

Timothy Russell; Blake Heller; David A. Jack; Douglas E. Smith. 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. Journal of Composites Science 2018, 2, 26 .

AMA Style

Timothy Russell, Blake Heller, David A. Jack, Douglas E. Smith. 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. Journal of Composites Science. 2018; 2 (2):26.

Chicago/Turabian Style

Timothy Russell; Blake Heller; David A. Jack; Douglas E. Smith. 2018. "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." Journal of Composites Science 2, no. 2: 26.

Article
Published: 16 February 2018 in Journal of Composites Science
Reads 0
Downloads 0

Short fiber-reinforced polymers have recently been introduced to large-scale additive manufacturing to improve the mechanical performances of printed-parts. As the short fiber polymer composite is extruded and deposited on a moving platform, velocity gradients within the melt orientate the suspended fibers, and the final orientation directly affects material properties in the solidified extrudate. This paper numerically evaluates melt rheology effects on predicted fiber orientation and elastic properties of printed-composites in three steps. First, the steady-state isothermal axisymmetric nozzle melt flow is computed, which includes the prediction of die swell just outside the nozzle exit. Simulations are performed with ANSYS-Polyflow, where we consider the effect of various rheology models on the computed outcomes. Here, we include Newtonian, generalized Newtonian, and viscoelastic rheology models to represent the melt flow. Fiber orientation is computed using Advani–Tucker fiber orientation tensors. Finally, elastic properties in the extrudate are evaluated based from predicted fiber orientation distributions. Calculations show that the Phan–Thien–Tanner (PTT) model yields the lowest fiber principal alignment among considered rheology models. Furthermore, the cross section averaged elastic properties indicate a strong transversely isotropic behavior in these composites, where generalized Newtonian models yield higher principal Young’s modulus, while the viscoelastic fluid models result in higher shear moduli.

ACS Style

Zhaogui Wang; Douglas E. Smith. Rheology Effects on Predicted Fiber Orientation and Elastic Properties in Large Scale Polymer Composite Additive Manufacturing. Journal of Composites Science 2018, 2, 10 .

AMA Style

Zhaogui Wang, Douglas E. Smith. Rheology Effects on Predicted Fiber Orientation and Elastic Properties in Large Scale Polymer Composite Additive Manufacturing. Journal of Composites Science. 2018; 2 (1):10.

Chicago/Turabian Style

Zhaogui Wang; Douglas E. Smith. 2018. "Rheology Effects on Predicted Fiber Orientation and Elastic Properties in Large Scale Polymer Composite Additive Manufacturing." Journal of Composites Science 2, no. 1: 10.

Journal article
Published: 25 September 2015 in Journal of Micro and Nano-Manufacturing
Reads 0
Downloads 0

This paper presents a computational approach for simulating the motion of nanofibers during fiber-filled composites processing. A finite element-based Brownian dynamics simulation (BDS) is proposed to solve for the motion of nanofibers suspended within a viscous fluid. We employ a Langevin approach to account for both hydrodynamic and Brownian effects. The finite element method (FEM) is used to compute the hydrodynamic force and torque exerted from the surrounding fluid. The Brownian force and torque are regarded as the random thermal disturbing effects which are modeled as a Gaussian process. Our approach seeks solutions using an iterative Newton–Raphson method for a fiber's linear and angular velocities such that the net forces and torques, including both hydrodynamic and Brownian effects, acting on the fiber are zero. In the Newton–Raphson method, the analytical Jacobian matrix is derived from our finite element model. Fiber motion is then computed with a Runge–Kutta method to update fiber position and orientation as a function of time. Instead of remeshing the fluid domain as a fiber migrates, the essential boundary condition is transformed on the boundary of the fluid domain, so the tedious process of updating the stiffness matrix of finite element model is avoided. Since the Brownian disturbance from the surrounding fluid molecules is a stochastic process, Monte Carlo simulation is used to evaluate a large quantity of motions of a single fiber associated with different random Brownian forces and torques. The final fiber motion is obtained by averaging numerous fiber motion paths. Examples of fiber motions with various Péclet numbers are presented in this paper. The proposed computational methodology may be used to gain insight on how to control fiber orientation in micro- and nanopolymer composite suspensions in order to obtain the best engineered products.

ACS Style

Dongdong Zhang; Douglas E. Smith. Finite Element-Based Brownian Dynamics Simulation of Nanofiber Suspensions Using Monte Carlo Method1. Journal of Micro and Nano-Manufacturing 2015, 3, 041007 .

AMA Style

Dongdong Zhang, Douglas E. Smith. Finite Element-Based Brownian Dynamics Simulation of Nanofiber Suspensions Using Monte Carlo Method1. Journal of Micro and Nano-Manufacturing. 2015; 3 (4):041007.

Chicago/Turabian Style

Dongdong Zhang; Douglas E. Smith. 2015. "Finite Element-Based Brownian Dynamics Simulation of Nanofiber Suspensions Using Monte Carlo Method1." Journal of Micro and Nano-Manufacturing 3, no. 4: 041007.