An official website of the United States government
Material extrusion (MEX) additive manufacturing has successfully fabricated assembly-free structures composed of different materials processed in the same manufacturing cycle. Materials with different mechanical properties can be employed for the fabrication of bio-inspired structures (i.e., stiff materials connected to soft materials), which are appealing for many fields, such as bio-medical and soft robotics. In the present paper, process parameters and 3D printing strategies are presented to improve the interfacial adhesion between carbon fiber-reinforced nylon (CFPA) and thermoplastic polyurethane (TPU), which are extruded in the same manufacturing cycle using a multi-material MEX setup. To achieve our goal, a double cantilever beam (DCB) test was used to evaluate the mode I fracture toughness. The results show that the application of a heating gun (assembled near the nozzle) provides a statistically significant increase in mean fracture toughness energy from 12.3 kJ/m2 to 33.4 kJ/m2. The underlying mechanism driving this finding was further investigated by quantifying porosity at the multi-material interface using an X-ray computed tomography (CT) system, in addition to quantifying thermal history. The results show that using both bead ironing and the hot air gun during the printing process leads to a reduction of 24% in the average void volume fraction. The findings from the DCB test and X-ray CT analysis agree well with the polymer healing theory, in which an increased thermal history led to an increased fracture toughness at the multi-material interface. Moreover, this study considers the thermal history of each printed layer to correlate the measured debonding energy with results obtained using the reptation theory.
more »
« less
Stereolithographic 3D Printing for Deterministic Control over Integration in Dual‐Material Composites
Abstract A rapid and facile approach to predictably control integration between two materials with divergent properties is introduced. Programmed integration between photopolymerizable soft and stiff hydrogels is investigated due to their promise in applications such as tissue engineering where heterogeneous properties are often desired. The spatial control afforded by grayscale 3D printing is leveraged to define regions at the interface that permit diffusive transport of a second material in‐filled into the 3D printed part. The printing parameters (i.e., effective exposure dose) for the resin are correlated directly to mesh size to achieve controlled diffusion. Applying this information to grayscale exposures leads to a range of distances over which integration is achieved with high fidelity. A prescribed finite distance of integration between soft and stiff hydrogels leads to a 33% increase in strain to failure under tensile testing and eliminates failure at the interface. The feasibility of this approach is demonstrated in a layer‐by‐layer 3D printed part fabricated by stereolithography, which is subsequently infilled with a soft hydrogel containing osteoblastic cells. In summary, this approach holds promise for applications where integration of multiple materials and living cells is needed by allowing precise control over integration and reducing mechanical failure at contrasting material interfaces.
more »
« less
- Award ID(s):
- 1826454
- PAR ID:
- 10460477
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials Technologies
- Volume:
- 4
- Issue:
- 11
- ISSN:
- 2365-709X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Polymer composites are becoming an important class of materials for a diversified range of industrial applications due to their unique characteristics and natural and synthetic reinforcements. Traditional methods of polymer composite fabrication require machining, manual labor, and increased costs. Therefore, 3D printing technologies have come to the forefront of scientific, industrial, and public attention for customized manufacturing of composite parts having a high degree of control over design, processing parameters, and time. However, poor interfacial adhesion between 3D printed layers can lead to material failure, and therefore, researchers are trying to improve material functionality and extend material lifetime with the addition of reinforcements and self-healing capability. This review provides insights on different materials used for 3D printing of polymer composites to enhance mechanical properties and improve service life of polymer materials. Moreover, 3D printing of flexible energy-storage devices (FESD), including batteries, supercapacitors, and soft robotics using soft materials (polymers), is discussed as well as the application of 3D printing as a platform for bioengineering and earth science applications by using a variety of polymer materials, all of which have great potential for improving future conditions for humanity and planet Earth.more » « less
-
Abstract Among the wide range of additive manufacturing — or “three-dimensional (3D) printing” — technologies, “material jetting” approaches are distinctively suited for multi-material fabrication. Because material jetting strategies, such as “PolyJet 3D printing”, harness inkjets that allow for multiple photopolymer droplets (and sacrificial support materials) to be dispensed in parallel to build 3D objects, distinct materials with unique properties can be readily unified in a single print akin to combining multiple-colored inks using a conventional 2D color printer. Although researchers have leveraged this multi-material capability to achieve, for example, 3D functionally graded and bi-material composite systems, there are cases in which the interface between distinct materials can become a key region of mechanical failure if not designed properly. To elucidate potential design factors that contribute to such failure modes, here we investigate the relationship between the interface design and tensile mechanical failure dynamics for PolyJet-printed bi-material coupons. Experimental results for a select set of bi-material sample designs that were 3D printed using a Stratasys Objet500 Connex3 PolyJet 3D printer and subjected to uniaxial tensile testing using a Tinius Olsen H25K-T benchtop universal testing machine under uniaxial strain revealed that increasing the surface contact area between two distinct materials via changes in geometric design does not necessarily increase the interface strength based on the length scales and loading conditions investigated in the current study and that further studies of the role of multi-material geometric designs in interface integrity are warranted to understand potential mechanisms underlying these results. Given the increasing interest in material jetting — and PolyJet 3D printing in particular — as a pathway to multi-material manufacturing in fields including robotics and fluidic circuitry, this study suggests that multi-material interface geometry should be considered appropriately for future applications.more » « less
-
3D‐printed polymer blends with programmable mechanical and compositional heterogeneity were fabricated using grayscale digital light processing by spatially modulating the intensity of light during printing and swelling the resulting part with a second monomer. A rubbery poly(ethylene glycol) diacrylate functionally graded print is variably swollen with acrylamide monomer as a function of crosslinking density. Following a secondary polymerization, a 3D‐printed functionally graded blend with regions of varying composition and stiffness was formed. A deterministic model for polymer conversion informs printing conditions to correspond with predicted material properties based upon local volume fractions of the two materials. Upon the secondary polymerization, two networks are present within the printed structure including glassy and rubbery regions. The compressive moduli of local regions within prints ranges from 76 to 200 MPa and measured moduli of the structures agree with predicted values acquired using finite element analysis. A lattice structure with prescribed local stiffness printed using grayscale exposures deforms differentially when compressed. Advantageously, local dimensional deformations caused by the removal of the unreacted printing monomer are eliminated due to the introduction of the second polymer. This method provides predictive control over local mechanical properties and high shape precision while maintaining the simplicity of vat photopolymerization.more » « less
-
Abstract Thermoplastic elastomers (TPEs) are nanostructured, melt‐processable, elastomeric block copolymers. When TPEs that form cylindrical or lamellar nanostructures are macroscopically oriented, their material properties can exhibit several orders of magnitude of anisotropy. Here it is demonstrated that the flows applied during the 3D printing of a cylinder‐forming TPE enable hierarchical control over material nanostructure and function. It is demonstrated that 3D printing allows for control over the extent of nanostructural and mechanical anisotropy and that thermal annealing of 3D printed structures leads to highly anisotropic properties (up to 85 × anisotropic tensile modulus). This approach is leveraged to print functional soft 3D architectures with tunable local and macroscopic mechanical responses. Further, these printed TPEs intrinsically achieve melt‐reprocessability over multiple cycles, reprogrammability, and robust self‐healing via a brief period of thermal annealing, enabling facile fabrication of highly tunable, robust, and recyclable soft architectures.more » « less
