The integration of 3D printed sensors into hosting structures has become a growing area of research due to simplified assembly procedures, reduced system complexity, and lower fabrication cost. Embedding 3D printed sensors into structures or bonding the sensors on surfaces are the two techniques for the integration of sensors. This review extensively discusses the fabrication of sensors through different additive manufacturing techniques. Various additive manufacturing techniques dedicated to manufacture sensors as well as their integration techniques during the manufacturing process will be discussed. This review will also discuss the basic sensing mechanisms of integrated sensors and their applications. It has been proven that integrating 3D printed sensors into infrastructures can open new possibilities for research and development in additive manufacturing and sensor materials for smart goods and the Internet of Things.

This research presents a simple method to additively manufacture Cone 5 porcelain clay ceramics by using the direct ink-write (DIW) printing technique. DIW has allowed the application of extruding highly viscous ceramic materials with relatively high-quality and good mechanical properties, which additionally allows a freedom of design and the capability of manufacturing complex geometrical shapes. Clay particles were mixed with deionized (DI) water at different ratios, where the most suitable composition for 3D printing was observed at a 1:5 w/c ratio (16.2 wt.%. of DI water). Differential geometrical designs were printed to demonstrate the printing capabilities of the paste. In addition, a clay structure was fabricated with an embedded wireless temperature and relative humidity (RH) sensor during the 3D printing process. The embedded sensor read up to 65% RH and temperatures of up to 85 °F from a maximum distance of 141.7 m. The structural integrity of the selected 3D printed geometries was confirmed through the compressive strength of fired and non-fired clay samples, with strengths of 70 MPa and 90 MPa, respectively. This research demonstrates the feasibility of using the DIW printing of porcelain clay with embedded sensors, with fully functional temperature- and humidity-sensing capabilities.

Laser Powder Bed Fusion (LPBF) is a widely used additive manufacturing technique for powder-based polymers and metallic materials. Thermoplastics like Polyamide 12 and Polyamide 6 are commonly used in LPBF; thermosetting polymers are gaining attention due to their superior stability. Epoxies are a popular thermoset, but some exhibit low physical properties and brittleness, leading to reduced toughness. The work presented in this paper explores the effect of using short carbon fibers (CF) as additives to epoxy-based thermosetting material on physical and thermomechanical properties. A total of six epoxy thermoset/CF composite powder blends were prepared by varying reinforcing materials weight percentages (0 wt%, 0.3 wt%, 0.6 wt%, 1 wt%, 5 wt%, and 10 wt%). Tensile, four-point bending, and dynamic mechanical analysis (DMA) test samples were printed using the LPBF technique. Significant improvements in the physical and thermomechanical properties were obtained in the thermoset composites with 5 wt% of CF due to good adhesion between reinforcing materials and the matrix and a low level of porosity. Fracture surface analysis was performed via scanning electron microscopy (SEM), which provided insight into the influence of CF on the properties of thermosetting composites. The findings of this research demonstrate the feasibility of improving the inferior physical and thermomechanical properties of 3D-printed CF-reinforced epoxy. With a certain amount of CF reinforcement, Young’s modulus and fracture modulus can be increased by around 52% and 259%, respectively.

The ever-changing nature of the power industry will require the implementation of hybrid energy systems. Integration of tightly coupled components in hybrids often involves the diversion of exhaust gas flow. An innovative smart material actuation technology is proposed to replace traditional electro-mechanical actuated valve mechanisms with lighter and less expensive actuators. A shape memory alloy (SMA) spring-actuated valve was designed for high-temperature service to demonstrate the promise of smart materials in control valve applications. With SMA springs only generating a maximum force of 3.2 N, an innovative valve design was necessary. To demonstrate the concept, a 3-inch Nominal Pipe Size valve was designed, and 3D printed using the stereolithography technique. Increasing the electrical current to actuate the SMA springs reduced actuation time. The maximum current of 10 A produced the lowest actuation time of 2.85 s, with an observed maximum stroke rate of more than 100 stroke completion %/s (considering actuation open/close as 100% stroke) at the midrange. The final assembly of the valve was estimated to provide a cost reduction of more than 30% and a weight reduction of more than 80% compared to the other available automatic valves in the present market.

Recently, the manufacturing of porous polydimethylsiloxane (PDMS) with engineered porosity has gained considerable interest due to its tunable material properties and diverse applications. An innovative approach to control the porosity of PDMS is to use transient liquid phase water to improve its mechanical properties, which has been explored in this work. Adjusting the ratios of deionized water to the PDMS precursor during blending and subsequent curing processes allows for controlled porosity, yielding water emulsion foam with tailored properties. The PDMS-to-water weight ratios were engineered ranging from 100:0 to 10:90, with the 65:35 specimen exhibiting the best mechanical properties with a Young’s Modulus of 1.17 MPa, energy absorption of 0.33 MPa, and compressive strength of 3.50 MPa. This led to a porous sample exhibiting a 31.46% increase in the modulus of elasticity over a bulk PDMS sample. Dowsil SE 1700 was then added, improving the storage capabilities of the precursor. The optimal storage temperature was probed, with −60 °C resulting in great pore stability throughout a three-week duration. The possibility of using these water emulsion foams for paste extrusion additive manufacturing (AM) was also analyzed by implementing a rheological modifier, fumed silica. Fumed silica’s impact on viscosity was examined, revealing that 9 wt% of silica demonstrates optimal rheological behaviors for AM, bearing a viscosity of 10,290 Pa·s while demonstrating shear-thinning and thixotropic behavior. This study suggests that water can be used as pore-formers for PDMS in conjunction with AM to produce engineered materials and structures for aerospace, medical, and defense industries as sensors, microfluidic devices, and lightweight structures.

Hollow polymer microspheres with superior elastic properties, high thermal stability, and energy absorbance capabilities are essential in many applications where shock and vibration need to be mitigated, such as in civil, medical, and defense industries. In this paper, the synthesis, fabrication, and characterization of hollow thermoset microspheres for syntactic polymer foam were studied. The hollow polymer microspheres (HPMs) were made by developing core–shell composites and thermally removing the polystyrene core to yield a polysiloxane shell. The HPMs were embedded into a polydimethylsiloxane (PDMS) matrix to form a polymer syntactic foam. The mechanical energy absorption characteristic of polymer syntactic foams was measured by cyclic uniaxial compression testing following ASTM 575. The engineered compression response was demonstrated by fabricating and testing syntactic foams with different porosities, ranging from a 50 vol% to 70 vol% of HPMs. Through scanning electron microscopy (SEM), we observed that the HPM contributes to the energy absorption of the syntactic foam. Moreover, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) determined the necessity of a profound study to understand the effects of varying HPM synthesis parameters, as well as the syntactic foam fabrication methods. It was shown that the compressive modulus and toughness can be increased by 20% using a 70 vol% of porosity with synthesized HPM syntactic foams over bulk PDMS. We also found that the energy absorbed increased by 540% when using a 50 vol% of porosity with fabricated HPM-PDMS syntactic foams.