More Like this

1. Effects of infill patterns on the strength and stiffness of 3D printed topologically optimized geometries

   https://doi.org/10.1108/RPJ-11-2019-0290  

   Hmeidat, Nadim S. ; Brown, Bailey ; Jia, Xiu ; Vermaak, Natasha ; Compton, Brett ( August 2021 , Rapid Prototyping Journal)

   Purpose Mechanical anisotropy associated with material extrusion additive manufacturing (AM) complicates the design of complex structures. This study aims to focus on investigating the effects of design choices offered by material extrusion AM – namely, the choice of infill pattern – on the structural performance and optimality of a given optimized topology. Elucidation of these effects provides evidence that using design tools that incorporate anisotropic behavior is necessary for designing truly optimal structures for manufacturing via AM. Design/methodology/approach A benchmark topology optimization (TO) problem was solved for compliance minimization of a thick beam in three-point bending and the resulting geometry was printed using fused filament fabrication. The optimized geometry was printed using a variety of infill patterns and the strength, stiffness and failure behavior were analyzed and compared. The bending tests were accompanied by corresponding elastic finite element analyzes (FEA) in ABAQUS. The FEA used the material properties obtained during tensile and shear testing to define orthotropic composite plies and simulate individual printed layers in the physical specimens. Findings Experiments showed that stiffness varied by as much as 22% and failure load varied by as much as 426% between structures printed with different infill patterns. The observed failure modes weremore »also highly dependent on infill patterns with failure propagating along with printed interfaces for all infill patterns that were consistent between layers. Elastic FEA using orthotropic composite plies was found to accurately predict the stiffness of printed structures, but a simple maximum stress failure criterion was not sufficient to predict strength. Despite this, FE stress contours proved beneficial in identifying the locations of failure in printed structures. Originality/value This study quantifies the effects of infill patterns in printed structures using a classic TO geometry. The results presented to establish a benchmark that can be used to guide the development of emerging manufacturing-oriented TO protocols that incorporate directionally-dependent, process-specific material properties.« less
2. Behavior of polyhedral built-up glass compression members

   Yost, Joseph Robert ; Akbarzadeh, Masoud ; Bolhassani, Mohammad ; Ryan, Liam ; Schneider, Jens ; Chhadeh, Philipp Amir ( July 2021 , International Conference on Civil Engineering and Architectural Design)

   This research presents an experimental program executed to understand the strength and stiffness properties of hollow built-up glass compression members that are intended for use in the modular construction of all glass, compression-dominant, shell-type structures. The proposed compression-dominant geometric form has been developed using the methods of form finding and three-dimensional graphical statics. This research takes the first steps towards a new construction methodology for glass structures where individual hollow glass units (HGU) are assembled using an interlocking system to form large, compression-dominant, shell-type structures, thereby exploiting the high compression strength of glass. In this study, an individual HGU has an elongated hexagonal prism shape and consists of two deck plates, two long side plates, and four short side plates, as is shown in Figure 1. Connections between glass plates are made using a two-sided transparent structural adhesive tape. The test matrix includes four HGUs, two each fabricated with 1 mm and 2 mm thick adhesive tape. All samples are dimensioned 64 cm on the long axis of symmetry, 51 cm on the short axis of symmetry, and are 10 cm in width. Glass plates are all 10 mm thick annealed float glass with geometric fabrication done using 5-axis abrasivemore »water jet cutting. HGU assembly is accomplished using 3D printed truing clips and results in a rigid three-dimensional glass frame. Testing was done with the HGU oriented such that load was introduced on the short side edges of the two deck plates, resulting in an asymmetric load-support condition. A soft interface material was used between the HGU and steel plates of the hydraulic actuator and support for the purpose of avoiding premature cracking from local stress concentrations on the glass edges at the load and support locations. Force was applied in displacement control at 0.25 mm/minute with a full array of displacement and strain sensors. Test results for load vs. center deck plate transverse deflection are shown in Figure 2. All samples failed explosively by flexural buckling with no premature cracking on the load and support edges of the deck plates. Strain and deformation data clearly show the presence of second-order behavior resulting from bending deformation perpendicular to the plane of the deck plates. In general, linear axial behavior transitions to nonlinear second-order behavior, with increasing rates in deflection and strain growth, ultimately ending in glass fracture on the tension surfaces of the buckled deck plates. The failure resulted in near-complete disintegration of the deck plates, but with no observable cracking in any side plates and a secure connection on all adhesive tape. Results of the experimental program clearly demonstrate the feasibility of using HGUs for modular construction of compression dominant all-glass shell-type structures. This method of construction can significantly reduce the self-weight of the structure, and it will inspire the use of sustainable materials in the construction of efficient structures.« less
3. Leveraging Geometry to Enable High-Strength Continuum Robots

   https://doi.org/10.3389/frobt.2021.629871  

   Childs, Jake A. ; Rucker, Caleb ( February 2021 , Frontiers in Robotics and AI)

   Developing high-strength continuum robots can be challenging without compromising on the overall size of the robot, the complexity of design and the range of motion. In this work, we explore how the load capacity of continuum robots can drastically be improved through a combination of backbone design and convergent actuation path routing. We propose a rhombus-patterned backbone structure composed of thin walled-plates that can be easily fabricated via 3D printing and exhibits high shear and torsional stiffness while allowing bending. We then explore the effect of combined parallel and converging actuation path routing and its influence on continuum robot strength. Experimentally determined compliance matrices are generated for straight, translation and bending configurations for analysis and discussion. A robotic actuation platform is constructed to demonstrate the applicability of these design choices.
4. Simulations of dynamically cross-linked actin networks: Morphology, rheology, and hydrodynamic interactions

   https://doi.org/10.1371/journal.pcbi.1009240  

   Maxian, Ondrej ; Peláez, Raúl P. ; Mogilner, Alex ; Donev, Aleksandar ( December 2021 , PLOS Computational Biology)

   Merks, Roeland M.H. (Ed.)

   Cross-linked actin networks are the primary component of the cell cytoskeleton and have been the subject of numerous experimental and modeling studies. While these studies have demonstrated that the networks are viscoelastic materials, evolving from elastic solids on short timescales to viscous fluids on long ones, questions remain about the duration of each asymptotic regime, the role of the surrounding fluid, and the behavior of the networks on intermediate timescales. Here we perform detailed simulations of passively cross-linked non-Brownian actin networks to quantify the principal timescales involved in the elastoviscous behavior, study the role of nonlocal hydrodynamic interactions, and parameterize continuum models from discrete stochastic simulations. To do this, we extend our recent computational framework for semiflexible filament suspensions, which is based on nonlocal slender body theory, to actin networks with dynamic cross linkers and finite filament lifetime. We introduce a model where the cross linkers are elastic springs with sticky ends stochastically binding to and unbinding from the elastic filaments, which randomly turn over at a characteristic rate. We show that, depending on the parameters, the network evolves to a steady state morphology that is either an isotropic actin mesh or a mesh with embedded actin bundles. For differentmore »degrees of bundling, we numerically apply small-amplitude oscillatory shear deformation to extract three timescales from networks of hundreds of filaments and cross linkers. We analyze the dependence of these timescales, which range from the order of hundredths of a second to the actin turnover time of several seconds, on the dynamic nature of the links, solvent viscosity, and filament bending stiffness. We show that the network is mostly elastic on the short time scale, with the elasticity coming mainly from the cross links, and viscous on the long time scale, with the effective viscosity originating primarily from stretching and breaking of the cross links. We show that the influence of nonlocal hydrodynamic interactions depends on the network morphology: for homogeneous meshworks, nonlocal hydrodynamics gives only a small correction to the viscous behavior, but for bundled networks it both hinders the formation of bundles and significantly lowers the resistance to shear once bundles are formed. We use our results to construct three-timescale generalized Maxwell models of the networks.« less
5. A study on Residual Drift and Concrete Strains in Unbonded Post-Tensioned Precast Rocking Walls

   Sharma, Sumedh ; Aaleti, Sriram ( June 2019 , Proceedings of the ... Canadian Conference on Earthquake Engineering)

   Modern seismic resistant design has been focusing on development of cost effective structural systems which experience minimal damage during an earthquake. Unbonded post-tensioned precast concrete walls provide a suitable solution due to their self-centering behavior and their ability to undergo large nonlinear deformation with minimal damage. Several experimental and analytical investigation focusing on lateral load resisting behavior of unbonded post-tensioned precast walls has been carried out in the past two decades. These investigations have primarily focused on lateral load resistance, self-centering capacity, energy dissipation and extent of damage in confined concrete region of the wall system. Past experimental results have shown that self-centering capacity of the wall system decreases at higher lateral drifts. Particularly, rocking walls with higher energy dissipation capacity, sustain considerable residual displacement. This residual displacement in the wall system may affect the ability of the entire structure to re-center. Though increasing initial prestressing force helps in reducing residual drift, it also subjects concrete to increased axial compressive stress which may lead to premature strength degradation of confined concrete in rocking corners. Accurate prediction of expected concrete strains in confined regions during increasing drift cycle is critical in design of such wall systems. Simplified design procedures available inmore »literature assume different values for plastic hinge length to estimate critical concrete strain values. The results from the experimental tests available in literature were analyzed, to understand the effects of energy dissipating elements on residual drift and to examine the accuracy of simplified design procedures in predicting critical concrete strain. Based on the findings, recommendations are made on design of energy dissipating elements and plastic hinge length for unbonded post-tensioned precast rocking walls.« less