An official website of the United States government
Abstract Cracking during sintering is a common problem in powder processing and is usually caused by constraint that prevents the sintering material from shrinking in one or more directions. Different factors influence sintering‐induced cracking, including temperature schedule, packing density, and specimen geometry. Here we use the discrete element method to directly observe the stress distribution and sinter‐cracking behavior in edge notched panels sintered under a uniaxial restraint. This geometry allows an easy comparison with traditional fracture mechanics parameters, facilitating analysis of sinter‐cracking behavior. We find that cracking caused by self‐stress during sintering resembles the growth of creep cracks in fully dense materials. By deriving the constrained densification rate from the appropriate constitutive equations, we discover that linear shrinkage transverse to the loading axis is accelerated by a contribution from the effective Poisson's ratio of a sintering solid. Simulation of different notch geometries and initial relative densities reveals conditions that favor densification and minimize crack growth, alluding to design methods for avoiding cracking in actual sintering processes. We combine the far‐field stress and crack length to compute the net section stress, finding that it characterizes the stress profile between the notches and correlates with the sinter‐crack growth rate, demonstrating its potential to quantitatively describe sinter‐cracking.
more »
« less
Aspects of sinter-cracking in binder jet 3D printed parts
Binder jet three-dimensional (3D) printing is a scalable, potentially low-cost additive manufacturing route able to process materials not attainable to other techniques, especially nonweldable materials. It relies on postprocess sintering to achieve final properties but encounters problems with distortion and cracking during sintering. The present work seeks to understand how part design geometry and 3D printing build orientation influence cracking during sintering, with the goal of mitigating the problem. In situ monitoring experiments reveal how sinter-cracks initiate and grow in 3D-printed notched panel specimens during densification. Different design geometries and build directions are tested to identify sinter-crack-resistant regimes.
more »
« less
- Award ID(s):
- 1826064
- PAR ID:
- 10389165
- Editor(s):
- Shamsaei Nima, Seifi Mohsen
- Date Published:
- Journal Name:
- Progress in Additive Manufacturing 2020
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Flexible thermoelectric (TE) devices hold great promise for energy harvesting and cooling applications, with increasing significance to serve as perpetual power sources for flexible electronics and wearable devices. Despite unique and superior TE properties widely reported in nanocrystals, transforming these nanocrystals into flexible and functional forms remains a major challenge. Herein, demonstrated is a transformative 3D conformal aerosol jet printing and rapid photonic sintering process to print and sinter solution‐processed Bi2Te2.7Se0.3nanoplate inks onto virtually any flexible substrates. Within seconds of photonic sintering, the electrical conductivity of the printed film is dramatically improved from nonconductive to 2.7 × 104S m−1. The films demonstrate a room temperature power factor of 730 µW m−1K−2, which is among the highest values reported in flexible TE films. Additionally, the film shows negligible performance changes after 500 bending cycles. The highly scalable and low‐cost fabrication process paves the way for large‐scale manufacturing of flexible devices using a variety of high‐performing nanoparticle inks.more » « less
-
Laser based additive manufacturing (AM) methods, that incorporate a high-density laser to sinter, melt, or solidify the desired material, have developed into an ideal technology for the design and fabrication of robust and highly customizable functional devices which aim to address key challenges in the aerospace, biomedical, and defense sectors. Recent advancements in powder bed fusion (PBF) approaches, such as selective laser sintering (SLS) and melting (SLM) have significantly improved the range of printable materials, minimum feature size, and microstructure evolution, endowing precise control over the physical properties of the final printed part. Furthermore, studies on novel photoresist materials and laser scanning strategies used during multiphoton lithography (MPL) approaches indicated that nanoscale spatial resolution could be achieved, allowing for the design of intricate biomedical implants or smooth optical devices. This chapter focuses on an extensive review of current research being conducted on laser-based AM technologies highlighting the current compatible materials and applications of SLS, SLM, and MLP printed functional devices. Future perspectives and notable challenges of the laser-based AM technologies are discussed in detail with the purpose of identifying critical research areas for each methodology.more » « less
-
Biocompatible polymers have emerged as essential materials in medical 3D printing, enabling the fabrication of scaffolds, tissue constructs, drug delivery systems, and biosensors for applications in and on the human body. This review aims to provide a comprehensive overview of the current state of 3D-printable biocompatible polymers and their composites, with an emphasis on their processing methods, properties, and biomedical uses. The scope of this work includes both natural and synthetic biocompatible polymers, polymer–nanocomposite systems, and bioinks that do not require photo initiators. The relevant literature was critically examined to classify materials by type, evaluate their compatibility with major 3D printing techniques such as stereolithography, selective laser sintering, and fused deposition modeling, and assess their performance in various medical applications. Key findings highlight that reinforced polymer composites, tailored surface chemistries, and hybrid printing strategies significantly expand the range of functional, customizable, and affordable biomedical devices. This review concludes by discussing present-day applications and emerging trends, underscoring that 3D-printable biocompatible polymers are rapidly transitioning from research to clinical practice, offering transformative potential for patient-specific healthcare solutions.more » « less
-
Abstract Three-dimensional (3D) printing of metal components through powder bed fusion, material extrusion, and vat photopolymerization, has attracted interest continuously. Particularly, extrusion-based and photopolymerization-based processes employ metal particle-reinforced polymer matrix composites (PMCs) as raw materials. However, the resolution for extrusion-based printing is limited by the speed-accuracy tradeoff. In contrast, photopolymerization-based processes can significantly improve the printing resolution, but the filler loading of the PMC is typically low due to the critical requirement on raw materials’ rheological properties. Herein, we develop a new metal 3D printing strategy by utilizing micro-continuous liquid interface printing (μCLIP) to print PMC resins comprising nanoporous copper (NP-Cu) powders. By balancing the need for higher filler loading and the requirements on rheological properties to enable printability for the μCLIP, the compositions of PMC resin were optimized. In detail, the concentration of the NP-Cu powders in the resins can reach up to 40 wt% without sacrificing the printability and printing speed (10 μm·s−1). After sintering, 3D copper structures with microscale features (470 ± 140 μm in diameter) manifesting an average resistivity of 150 kΩ·mm can be realized. In summary, this new strategy potentially benefits the rapid prototyping of metal components with higher resolution at faster speeds.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- The DOI is not currently available.
