skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Anisotropy in Additively Manufactured Concrete Specimens under Compressive Loading—Quantification of the Effects of Layer Height and Fiber Reinforcement
Title: Anisotropy in Additively Manufactured Concrete Specimens under Compressive Loading—Quantification of the Effects of Layer Height and Fiber Reinforcement
This paper analyzes the effect of print layer heights and loading direction on the compressive response of plain and fiber-reinforced (steel or basalt fiber) 3D printed concrete. Slabs with three different layer heights (6, 13, and 20 mm) are printed, and extracted cubes are subjected to compression (i) along the direction of printing, (ii) along the direction of layer build-up, and (iii) perpendicular to the above two directions. Digital image correlation (DIC) is used as a non-contact means to acquire the strain profiles. While the 3D printed specimens show lower strengths, as compared to cast specimens, when tested in all three directions, this effect can be reduced through the use of fiber reinforcement. Peak stress and peak strain-based anisotropy coefficients, which are linearly related, are used to characterize and quantify the directional dependence of peak stress and strain. Interface-parallel cracking is found to be the major failure mechanism, and anisotropy coefficients increase with an increase in layer height, which is attributable to the increasing significance of interfacial defects. Thus, orienting the weaker interfaces appropriately, through changes in printing direction, or strengthening them through material modifications (such as fiber reinforcement) or process changes (lower layer height, enables attainment of near-isotropy in 3D printed concrete elements.  more » « less
Award ID(s):
2020095
PAR ID:
10482368
Author(s) / Creator(s):
; ;
Publisher / Repository:
MDPI
Date Published:
Journal Name:
Materials
Volume:
16
Issue:
15
ISSN:
1996-1944
Page Range / eLocation ID:
5488
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; (, Polymers)
    One of the fundamental issues in the Fused Filament Fabrication (FFF) additive manufacturing process lies in the mechanical property anisotropy where the strength of the FFF-3D printed part in the build-direction can be significantly lower than that in other directions. The physical phenomenon that governs this issue is the coupled effect of macroscopic thermal mechanical issues associated with the thermal history of the interface, and the microscopic effect of the polymer microstructure and mass transfer across interfaces. In this study it was found that the use of 34.4 kHz ultrasonic vibrations during FFF-3D printing results in an increase of up to 10% in the interlayer adhesion in Acrylonitrile Butadiene Styrene (ABS), comparing the printing in identical thermal conditions to that in conventional FFF printing. This increase in the interlayer adhesion strength is attributed to the increase in polymer reptation due to ultrasonic vibration-induced relaxation of the polymer chains from secondary interactions in the interface regions. 
    more » « less
  2. ; ; ; ; ; (, Applied Physics Letters)
    We designed and characterized a 3D printed acoustic shear wave polarization rotator (PR) based on the specific nature of the fused-deposition-modeling printing process. The principle of the PR is based on rotation of the polarization axis of a shear wave due to the gradual change in orientation of the axis of anisotropy along the direction of wave propagation of a printed layered structure. The component of the shear modulus parallel to the infilled lines within each layer is significantly higher than that in the perpendicular direction. As the PR was printing, a small angle between neighboring layers was introduced, resulting in a 3D helicoidal pattern of distribution of the axes of anisotropy. The polarization of the propagating shear wave follows this pattern leading to the rotation of the polarization axis by a desirable angle. The total rotation angle can be tuned by the number of printed layers. The fabricated [Formula: see text] rotators demonstrate high performance that can be improved by changing the infill fraction settings. 
    more » « less
  3. ; ; ; (, Journal of Geophysical Research: Solid Earth)
    Abstract The dynamics of Earth's D″ layer at the base of the mantle plays an essential role in Earth's thermal and chemical evolution. Mantle convection in D″ is thought to result in seismic anisotropy; therefore, observations of anisotropy may be used to infer lowermost mantle flow. However, the connections between mantle flow and seismic anisotropy in D″ remain ambiguous. Here, we calculate the present‐day mantle flow field in D″ using 3D global geodynamic models. We then compute strain, a measure of deformation, outside the two large‐low velocity provinces (LLVPs) and compare the distribution of strain with previous observations of anisotropy. We find that, on a global scale, D″ materials are advected toward the LLVPs. The strains of D″ materials generally increase with time along their paths toward the LLVPs and toward deeper depths, but regions far from LLVPs may develop relative high strain as well. Materials in D″ outside the LLVPs mostly undergo lateral stretching, with the stretching direction often aligning with mantle flow direction, especially in fast flow regions. In most models, the depth‐averaged strain in D″ is >0.5 outside the LLVPs, consistent with widespread observations of seismic anisotropy. Flow directions inferred from anisotropy observations often (but not always) align with predictions from geodynamic modeling calculations. 
    more » « less
  4. ; ; ; ; (, Polymer Composites)
    Abstract A ram extruder is described for high‐pressure extrusion of fully compounded thermoset rubber to achieve additive manufacturing. The extruder uses a piston driven by a geared stepper motor to provide volumetric displacement of the rubber charge residing in a temperature‐controlled barrel. Along with activators, accelerators, and a vulcanizing agent, the rubber compound is a formulation of 30 parts carbon black per hundred parts nitrile rubber. Sets of serpentine patterns are printed in parallel and transverse orientations relative to the load direction. From printing to post‐cure, the printed specimens exhibited linear shrinkage of 65% in the print direction. Although printed samples had relatively low void content compared with typical additively manufactured parts by material extrusion, significant decreases in the tensile properties were observed relative to compression‐molded specimens of the same rubber compound. The mean strain to failure was observed as 462% for compression‐molded samples, compared with 347% and 183% for printed specimens with parallel and transverse orientations. To reduce the shrinkage and increase the interfacial area between extruded roads, backstitch and sinewave diddling patterns were implemented to superimpose oscillatory motions along the print path with a periodicity of 1 mm. The specimens printed with the diddling patterns were observed to provide less shrinkage and improved properties compared to the regular serpentine patterns. The mean strain to failure in the transverse orientation, respectively, increased to 218% and 265% for the backstitch and sinewave patterns. Suggested future research is discussed, and the diddling program is provided in the appendix. 
    more » « less
  5. ; ; ; (, Journal of Manufacturing Science and Engineering)
    null (Ed.)
    Abstract Pellet-based extrusion deposition of carbon fiber-reinforced composites at high material deposition rates has recently gained much attention due to its applications in large-scale additive manufacturing. The mechanical and physical properties of large-volume components largely depend on their reinforcing fiber length. However, very few studies have been done thus far to have a direct comparison of additively fabricated composites reinforced with different carbon fiber lengths. In this study, a new additive manufacturing (AM) approach to fabricate long fiber-reinforced polymer (LFRP) was first proposed. A pellet-based extrusion deposition method was implemented, which directly used thermoplastic pellets and continuous fiber tows as feedstock materials. Discontinuous long carbon fibers, with an average fiber length of 20.1 mm, were successfully incorporated into printed LFRP samples. The printed LFRP samples were compared with short fiber-reinforced polymer (SFRP) and continuous fiber-reinforced polymer (CFRP) counterparts through mechanical tests and microstructural analyses. The carbon fiber dispersion, distribution of carbon fiber length and orientation, and fiber wetting were studied. As expected, a steady increase in flexural strength was observed with increasing fiber length. The carbon fibers were highly oriented along the printing direction. A more uniformly distributed discontinuous fiber reinforcement was found within printed SFRP and LFRP samples. Due to decreased fiber impregnation time and lowered impregnation rate, the printed CFRP samples showed a lower degree of impregnation and worse fiber wetting conditions. The feasibility of the proposed AM methods was further demonstrated by fabricating large-volume components with complex geometries. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email