Computational Investigation of the Post-yielding Behavior of 3D-Printed Polymer Lattice Structures

Sandwich structures are widely used due to their light weight, high specific strength, and high specific energy absorption. Three-dimensional (3D) printing has recently been explored for creating the lattice cores of these sandwich structures. Experimental evaluation of the mechanical response of lattice cell structures (LCSs) is expensive in time and materials. As such, the finite element analysis (FEA) can be used to predict the mechanical behavior of LCSs with many different design variations more economically. Though there have been several reports on the use of FEA to develop models for predicting the post-yielding stages of 3D-printed LCSs, they are still insufficient to be a more general purpose due to the limitations associated with the lattice prediction behavior of specific features, certain geometries, and common materials along with showing sometimes poor prediction due to the computationally cheap elements out of which these models have been composed in most cases. This study focuses on the response of different LCSs at post-yielding stages based on the hexahedral elements to capture accurately the behaviors of 3D-printed polymeric lattices made of the Acrylonitrile Butadiene Styrene material. For this reason, three types of lattices such as body centered cubic, tetrahedron with horizontal struts, and pyramidal are considered. The FEA models are developed to capture the post-yielding compressive behavior of these different LCSs. These models are used to understand and provide detailed information of the failure mechanisms and relation between post-yielding deformations and the topologies of the lattice. All of these configurations were tested before experimentally during compression in the z-direction under quasi-static conditions and are compared here with the FEA results. The post-yielding behavior obtained from FEA matches reasonably well with the experimental observations, providing the validity of the FEA models

Developing Scaling Laws to Predict Compressive Mechanical Properties and Determine Geometrical Parameters of Modified BCC Lattice Structures

The objective of this study is to develop generalized empirical closed-form equations to predict the compressive mechanical properties and determine geometrical parameters. To achieve that, 117 models are built and analyzed using ABAQUS/CAE 2016 to provide two types of reliable data: one for lattice mechanical properties based on finite element method and the other for geometrical parameters using the measurements of ABAQUS diagnostic tool. All the models are created by modifying the basic feature of body-centered cubic lattice structure based on a range of strut angles, a set of relative densities, and two design sets. Also, the influence of lattice cell tessellations and material distribution at strut intersections are considered within these models to provide accurate results. The first data set is fitted with the scaling laws, relating relative elastic modulus and stress with the relative density, to determine Gibson and Ashby\u27s coefficients. The second type of data regarding lattice geometries is correlated with the relative density to estimate actual lattice volume, strut radius, aspect ratio, and overall lattice volume. By this way, these equations can be used to predict directly the lattice characteristics and geometrical parameters without the need for ABAQUS. The results show that the generalized empirical closed-form equations can predict well both the lattice characteristics and geometries. In addition, the relative stresses and elastic modulus increase with increasing the strut angles since the main deformation mechanisms move toward stretch-dominated rather than bending. Besides, Gibson and Ashby\u27s coefficients along with the geometrical factors of aspect ratios are found to be approximately similar for both generations. This study contributes to developing efficient equations to provide the researchers with a preliminary insight about the best lattice design and its compatibility in a certain application before starting the fabrication process

Development and Application of a Computational Modeling Scheme for Periodic Lattice Structures

Sandwich structures are widely used for aerospace, marines and other applications due to their light-weight, strength, and strain energy absorption capability. The cores of the sandwich structure are typically fabricated by using high strength cellular materials such as aluminum and titanium alloys, or polymer foams, and honeycombs. Lattice cell structures (LCS) of different configurations such as body centered cubic (BCC), tetrahedron and pyramidal are being investigated as core material due to their design freedom and periodic nature. Due to the recent advent of additive manufacturing (AM), new research is being sought in the areas of designing and developing application-specific LCS configurations. However, experimental investigation of LCS is costly in time and materials. Therefore, in this dissertation, finite element models are developed using ABAQUS and validated according to previous experimental results to design application-specific LCS. First, an efficient and user-friendly tool was developed and this tool is called the Lattice Structure Designer (LSD). The LSD was developed from ABAQUS GUI and using Python scripting. This tool can be used to create the lattice models, define the materials, define the geometry, define the boundary conditions, apply loads, and submit the jobs to perform the computational analysis. The same tool can be used to access the database files and calculate any additional outputs. This ABAQUS plug-in has effectively helped to capture the responses beyond the plasticity levels and capture the failure mechanisms of the lattice structure. In this research, three types of lattices such as body centered cubic (BCC), tetrahedron with horizontal struts (TetH), and pyramidal (Pyr) are considered. These models are used to understand the failure mechanisms and relation between post-yielding deformations and the topologies of the lattice. All of these configurations were tested under compression in the z direction under quasi-static conditions and are compared with the FEA results. The post-yielding behavior obtained from FEA match reasonably well with the experimental observations providing the validity of the FEA models. Therefore, in this dissertation, finite element models are developed using ABAQUS and validated according to previous experimental results to design application-specific LCS. First, an efficient and user-friendly tool was developed and this tool is called the Lattice Structure Designer (LSD). The LSD was developed from ABAQUS GUI and using Python scripting. This tool can be used to create the lattice models, define the materials, define the geometry, define the boundary conditions, apply loads, and submit the jobs to perform the computational analysis. The same tool can be used to access the database files and calculate any additional outputs. This ABAQUS plug-in has effectively helped to capture the responses beyond the plasticity levels and capture the failure mechanisms of the lattice under compression and impact loads

ABAQUS Plug-In Finite Element Tool for Designing and Analyzing Lattice Cell Structures

This paper presents the development of a lattice structure design (LSD) tool for building and analyzing different configurations of 3D-printed lattice structure (LS). This tool was developed via ABAQUS graphical user interface (GUI) based on Python code. Due to the extensive research activities in the field of lattice design using experimental and computational methods, there is a high demand for finding new techniques to reduce the computational time and human effort. Also, several challenges were revealed while creating finite element models for lattices of complicated geometries. These models showed the capability for capturing the elastic and inelastic mechanical responses of LSs during the compression test. Consequently, the LSD tool was designed not only to build lattice structures in a short time and simple way, but also to analyze the associated compressive mechanical behavior that goes beyond initial yielding to cover the entire crushing behavior. This paper examined many challenges involved in generating and decomposing the lattice geometry, creating hexahedron elements and optimizing the mesh density, assigning and inserting the material type, activating the face recognition to define the boundary and loading conditions, and conducting linear and polar patterns. Finally, to demonstrate the effectiveness of the new approach in designing and analyzing LSs, finite element results were validated with the previous experimental findings

A Computational Approach in Understanding the Low-Velocity Impact Behavior and Damage of 3D-Printed Polymer Lattice Structures

The remarkable mechanical characteristics of sandwich lattice structures have attracted the attention of many researchers and make it a good candidate for various applications. However, there is limited published research concerning the development of general-purpose dynamic models mimicking the impact behavior of lattice configurations made from polymeric materials. As such, the main focus of this research is to develop efficient computational finite element models simulating the dynamic impact behavior of various lattice configurations embedded in sandwich panels that are made from Acrylonitrile Butadiene Styrene (ABS) material. In this case, the sandwich panel consists of a 3D-printed polymer lattice core covered with the skin of a Kevlar sheet. Four designs with different configurations of lattice structures were investigated experimentally in previous studies. The first configuration was the basic body centered cubic (BCC) with unit cell dimensions of 5 mm × 5 mm × 5 mm, and a strut diameter of 1 mm. The second configuration was produced by adding the vertical struts at alternative nodes layer by layer, referred to as BCCA. The third configuration was created by adding the struts with uniform gradient distributions, termed as BCCG. The last configuration was designed by adding vertical struts at all nodes on the BCC configuration, denoted as BCCV. In this research, the FEA software ABAQUS Explicit was used to model all four configurations under low-velocity impact loads. Then, the results from the FEA modeling of the four different sandwich structures were compared with the experimental observations. Significantly, the good agreement in the results between the FEA and the experimental work reveals the capability of the developed models to capture the dynamic impact behavior of various lattice configurations and is considered the main contribution of the current research. In addition, in situ deformation along with failure mechanisms, detailed information, visualization, and sufficient data of the lattice impact test has been obtained through the developed models. This in turn leads to saving human time and effort, providing better realization and deep analysis of impact deformation behavior reducing the size of the experimental work and the expenses associated with it

A Computational Approach in Understanding the Low-Velocity Impact Behavior and Damage of 3D-Printed Polymer Lattice Structures

The remarkable mechanical characteristics of sandwich lattice structures have attracted the attention of many researchers and make it a good candidate for various applications. However, there is limited published research concerning the development of general-purpose dynamic models mimicking the impact behavior of lattice configurations made from polymeric materials. As such, the main focus of this research is to develop efficient computational finite element models simulating the dynamic impact behavior of various lattice configurations embedded in sandwich panels that are made from Acrylonitrile Butadiene Styrene (ABS) material. In this case, the sandwich panel consists of a 3D-printed polymer lattice core covered with the skin of a Kevlar sheet. Four designs with different configurations of lattice structures were investigated experimentally in previous studies. The first configuration was the basic body centered cubic (BCC) with unit cell dimensions of 5 mm × 5 mm × 5 mm, and a strut diameter of 1 mm. The second configuration was produced by adding the vertical struts at alternative nodes layer by layer, referred to as BCCA. The third configuration was created by adding the struts with uniform gradient distributions, termed as BCCG. The last configuration was designed by adding vertical struts at all nodes on the BCC configuration, denoted as BCCV. In this research, the FEA software ABAQUS Explicit was used to model all four configurations under low-velocity impact loads. Then, the results from the FEA modeling of the four different sandwich structures were compared with the experimental observations. Significantly, the good agreement in the results between the FEA and the experimental work reveals the capability of the developed models to capture the dynamic impact behavior of various lattice configurations and is considered the main contribution of the current research. In addition, in situ deformation along with failure mechanisms, detailed information, visualization, and sufficient data of the lattice impact test has been obtained through the developed models. This in turn leads to saving human time and effort, providing better realization and deep analysis of impact deformation behavior reducing the size of the experimental work and the expenses associated with it

ABAQUS Plug-In Finite Element Tool for Designing and Analyzing Lattice Cell Structures

This paper presents the development of a lattice structure design (LSD) tool for building and analyzing different configurations of 3D-printed lattice structure (LS). This tool was developed via ABAQUS graphical user interface (GUI) based on Python code. Due to the extensive research activities in the field of lattice design using experimental and computational methods, there is a high demand for finding new techniques to reduce the computational time and human effort. Also, several challenges were revealed while creating finite element models for lattices of complicated geometries. These models showed the capability for capturing the elastic and inelastic mechanical responses of LSs during the compression test. Consequently, the LSD tool was designed not only to build lattice structures in a short time and simple way, but also to analyze the associated compressive mechanical behavior that goes beyond initial yielding to cover the entire crushing behavior. This paper examined many challenges involved in generating and decomposing the lattice geometry, creating hexahedron elements and optimizing the mesh density, assigning and inserting the material type, activating the face recognition to define the boundary and loading conditions, and conducting linear and polar patterns. Finally, to demonstrate the effectiveness of the new approach in designing and analyzing LSs, finite element results were validated with the previous experimental findings

Effect of Vertical Strut Arrangements on Compression Characteristics of 3D Printed Polymer Lattice Structures: Experimental and Computational Study

This paper discusses the behavior of the three-dimensional (3D) printed polymer lattice core structures during compressive deformation, by both physical testing and computer modeling. Four lattice configurations based on the body-centered cubic (BCC) unit cell were selected to investigate the effect of vertical strut arrangements on stiffness, failure load, and energy absorption per unit mass or the specific energy absorption (SEA). The basic BCC unit cell consists of struts connecting the body center to the corners of the cube. Three variations in the BCC configuration considered in this study are (1) BCCV, with vertical members connecting all nodes of the lattice, (2) BCCA, with vertical members in alternating layers of the lattice, and (3) BCCG, with a gradient in the number of vertical members increasing from none at the top layer to all vertical members at the bottom layer. The unit cell dimensions were 5mmx5mmx5mm with strut diameter of 1mm. The lattice was assembled with 5 cells in the x and y directions and 4 cells in the z direction. Specimens were first made by 3D printing by using a fused deposition modeling printer with acrylonitrile-butadiene-styrene thermoplastic. Specimens were then tested under compression in the z direction under quasi-static conditions. Finite element analysis was used to model the compressive behavior of the different lattice structures. Results from both experiments and finite element models show that the strength of the lattice structures is greater when vertical members are present, and the SEA depends on the lattice geometry and not its mass

Effect of Vertical Strut Arrangements on Compression Characteristics of 3D Printed Polymer Lattice Structures: Experimental and Computational Study

This paper discusses the behavior of the three-dimensional (3D) printed polymer lattice core structures during compressive deformation, by both physical testing and computer modeling. Four lattice configurations based on the body-centered cubic (BCC) unit cell were selected to investigate the effect of vertical strut arrangements on stiffness, failure load, and energy absorption per unit mass or the specific energy absorption (SEA). The basic BCC unit cell consists of struts connecting the body center to the corners of the cube. Three variations in the BCC configuration considered in this study are (1) BCCV, with vertical members connecting all nodes of the lattice, (2) BCCA, with vertical members in alternating layers of the lattice, and (3) BCCG, with a gradient in the number of vertical members increasing from none at the top layer to all vertical members at the bottom layer. The unit cell dimensions were 5mmx5mmx5mm with strut diameter of 1mm. The lattice was assembled with 5 cells in the x and y directions and 4 cells in the z direction. Specimens were first made by 3D printing by using a fused deposition modeling printer with acrylonitrile-butadiene-styrene thermoplastic. Specimens were then tested under compression in the z direction under quasi-static conditions. Finite element analysis was used to model the compressive behavior of the different lattice structures. Results from both experiments and finite element models show that the strength of the lattice structures is greater when vertical members are present, and the SEA depends on the lattice geometry and not its mass

Developing Scaling Laws to Predict Compressive Mechanical Properties and Determine Geometrical Parameters of Modified BCC Lattice Structures

The objective of this study is to develop generalized empirical closed-form equations to predict the compressive mechanical properties and determine geometrical parameters. To achieve that, 117 models are built and analyzed using ABAQUS/CAE 2016 to provide two types of reliable data: one for lattice mechanical properties based on finite element method and the other for geometrical parameters using the measurements of ABAQUS diagnostic tool. All the models are created by modifying the basic feature of body-centered cubic lattice structure based on a range of strut angles, a set of relative densities, and two design sets. Also, the influence of lattice cell tessellations and material distribution at strut intersections are considered within these models to provide accurate results. The first data set is fitted with the scaling laws, relating relative elastic modulus and stress with the relative density, to determine Gibson and Ashby\u27s coefficients. The second type of data regarding lattice geometries is correlated with the relative density to estimate actual lattice volume, strut radius, aspect ratio, and overall lattice volume. By this way, these equations can be used to predict directly the lattice characteristics and geometrical parameters without the need for ABAQUS. The results show that the generalized empirical closed-form equations can predict well both the lattice characteristics and geometries. In addition, the relative stresses and elastic modulus increase with increasing the strut angles since the main deformation mechanisms move toward stretch-dominated rather than bending. Besides, Gibson and Ashby\u27s coefficients along with the geometrical factors of aspect ratios are found to be approximately similar for both generations. This study contributes to developing efficient equations to provide the researchers with a preliminary insight about the best lattice design and its compatibility in a certain application before starting the fabrication process