Here, we present the implementation and evaluation of nondeterministic automated image analysis methods, based on deep learning (DL) equipped with uncertainty quantification (UQ), for high-throughput, generalizable, uncertainty aware segmentation of high-resolution micro-computed tomography (mu CT) of advanced composite microdamage. The complex, label-sparse (<<1% of scan volume) datasets used are composed of publicly available trainedhuman-labeled 2D tomograms that capture progressive microdamage (via mu CT scanning while under increasing tensile loading) in two different aerospace-grade carbon fiber/epoxy laminates. The Monte Carlo Dropout Network (MCDN), a recent implementation of an uncertainty-aware/nondeterministic fully convolutional neural network, was studied during training, validation, and testing stages to assess the effects of key hyperparameters, such as spatial dropout factor, class weighting of the loss function, output layer bias initialization, and initial learning rate, on MCDN learning and nondeterministic predictive performance and UQ for binary damage segmentation. Compared to a baseline deterministic MCDN model (dropout factor of 0), we find generally that even MCDN models featuring a relatively high dropout factor up to 0.7 can effectively learn (generally within +/- 10% of the validation set performance of the deterministic model) and infer complex binary damage with acceptable levels of uncertainty/confidence, with training times being largely unaffected by the dropout extent. MCDN training performance was found to be highly sensitive to the initialization approach used for the output layer bias. Detailed assessments of the nondeterministic prediction accuracy and uncertainty for several MCDN models with different dropout factors showed a clear inverse relationship for all composites as dropout magnitude decreases between nondeterministic predictive accuracy (accuracy increases) and uncertainty (capacity decreases). This study presents a feasible approach to find an effective balance of nondeterministic predictive accuracy/UQ, which has not been reported previously for composites microstructural characterization and may provide guidance for developing UQbased active learning toward enhanced image-based materials modeling.

Bipolar plates (BPs) are essential multifunctional components in vanadium redox flow batteries (VRFBs) that require excellent electrical conductivity, low permeability, and strong solid support for the stack. However, conventional BPs are based on graphite sheets, which provide mechanical properties and corrosion resistance but have limitations in terms of electrical conductivity. Although carbon nanotubes (CNTs) have excellent properties, CNT composites with low CNT volume fractions (10-20%) have increased electrolyte permeability and limited electrical conductivity improvement, resulting in low durability and efficiency for VRFBs. This study proposes a novel concept of horizontally aligned CNT nanocomposite bipolar plate (HACN-BP) to address these issues. The HACN-BPs feature an optimized conduction path with a CNT volume fraction of 59%, resulting in reduced manufacturing time while demonstrating superior conductivity and permeability compared to conventional BPs. Furthermore, integrated HACN-BP mitigates ohmic loss that occurs in the BPs, thereby mitigating the potential drop by 40%. Therefore, the utilization of HACN-BP shows superior performance compared to recent studies, a substantial improvement of more than 6% in energy efficiency and 14% in capacity over conventional BP.

Nanocomposites of aligned boron nitride nanotubes (A-BNNTs) are envisioned as next-generation multifunctional materials due to the exceptional mechanical, optical, and thermal properties of hexagonal BNNTs, among others. Here we present optically-transparent polymer nanocomposites (PNCs) reinforced with A-BNNTs, using two structural epoxy matrices that are both optically transparent, including synthesis and characterization. Fourier Transform Infrared (FTIR) and Raman spectra show no evidence of nanofiber-matrix chemical interactions, however differential scanning calorimetry (DSC) indicates that polymer Tg is altered for both epoxies. Small-angle (SAXS) and wide-angle (WAXS) x-ray scattering indicates a high degree of BNNT alignment in the PNCs per Herman's orientation parameter. The A-BNNT reinforcement provides enhanced hardness and modulus, with nanoindentation revealing mechanical anisotropy that correlates with measured BNNT texture. Optical measurements in the UV-Vis range indicate that BNNT reinforcement does not significantly alter the absorbance of the polymers as might be expected due to the polymer-BNNT interfaces. This work establishes the first structure-property relations for controlled-morphology polymer nanocomposites (PNCs) with A-BNNTs, and provides a platform for further investigation including other multifunctional properties (such as piezoelectricity) and BNNT PNC process-structure relations at higher BNNT loading.

Interlaminar reinforcement, utilizing vertically aligned carbon nanotubes (VA-CNT), was realized for the first time with high-temperature aerospace carbon fiber reinforced plastic (CFRP) composites. Polyimide composites, widely used in high-temperature aerospace applications, have higher operating temperatures than epoxy systems (350-400 degrees C vs. 150-200 degrees C) due to their higher glass transition temperature (Tg), but suffer from lower toughness and reduced interlaminar properties. In prior work, employing VA-CNT arrays between plies has successfully toughened and strengthened the interlaminar region in aerospace epoxy CFRP, leading to broadly improved mechanical properties, including fatigue life. Here, two VA-CNT interlaminar reinforcing architectures are integrated with aerospace PI CFRP and show significant reinforcing effects. Both architectures, VA-CNTs (termed nanostitch) and a patterned and densified VA-CNT forest (termed buckled nanostitch), are integrated with PI CFRP. While maintaining the interlaminar thickness, 10 mu m thick VA-CNT films (nanostitch) show an increase in short-beam shear (SBS) strength by 22 % under static loading and 2-13 times increase in fatigue life under SBS fatigue loading. Toughness increases of 31 % and 30 % are observed in initiation and steady-state Mode I toughness, respectively, with the steady-state crack noted to bifurcate away from the reinforced inter- laminar region and into the intralaminar region. This study underscores the application of CNTs as reinforcement in relatively brittle high-temperature aerospace composite structures, such as aircraft engine components, space vehicle heat shields, and satellite structural elements.

The Mode I, Mode II, and mixed-mode interlaminar failure behavior of a thin-ply (54 gsm) carbon fiber-epoxy laminated composite reinforced by 20 μm tall z-direction-aligned carbon nanotubes (CNTs), comprising ∼50 billion CNT fibers per cm2, is analyzed following J-integral-based data reduction methods. The inclusion of aligned CNTs in the ply interfaces provides enhanced crack resistance, resulting in sustained crack deflection from the reinforced interlaminar region to the intralaminar region of the adjacent plies, i.e., the CNTs drive the crack from the interlaminar region into the plies. The CNTs do not appreciably increase the interlaminar thickness or laminate weight and preserve the intralaminar microfiber morphology. Improvements of 34 and 62% on the Mode I and Mode II initiation fracture toughness, respectively, are observed. This type of interlaminar nanoreinforcement effectively drives crack propagation from the interface to within the ply where the crack propagates parallel to the interlaminar region, providing new insight into previously reported strength and fatigue performance increases. These findings extend to industries where lightweight and durable materials are critical for improving the structural efficiency.

A novel high volume fraction horizontally-aligned carbon nanotubes (HA-CNTs) reinforced polybismaleimide (BMI) bulk nanocomposite laminate ( BNL) was developed towards achieving high mass-specific mechanical properties. Apart from the high strength and modulus, aligned CNT reinforced composites with mechanical anisotropy also exhibit multifunctional potential, such as electrical and thermal characteristics. CNTs have high electrical conductivity and a negative coefficient of thermal expansion in the axial direction. Past fabrication of CNT-reinforced polymer composites focused on random dispersions of nanofibers resulting in low packing density and agglomeration causing difficulty in realizing significant (non-isotropic) electrical and thermal properties. We report successful manufacturing of HA-CNT composite laminates containing uniformly aligned CNTs at unprecedented high volume fractions (similar to 50 vol%) using an aerospace-grade thermoset BMI polymer matrix. A square 4-point probe based on the modified Wesscher and Montgomery method was applied to measure the non-isotropic electrical conductivity and sheet resistance of the BNL, and Digital Image Correlation (DIC) was used to measure the coefficient of thermal expansion ( CTE). High electrical conductivity and anisotropy were observed for the BNL relative to other fiber-based and nanofiber-based composites, and a negative CTE near room temperature was observed for the HA-CNT/BMI nanocomposites. With the high specific strength, rapid manufacturing process, and multifunctionality of aligned CNTs, BMI thermoset BNL composites have the potential to replace neat polymer films in many aerospace applications.

Hierarchical nanoengineered composite laminates were created with through-thickness-aligned carbon nanotube (A-CNT) reinforcement of unidirectional carbon (micro) fiber/epoxy laminae in their failure-prone interlaminar regions, forming a multiscale "nanostitched" architecture. Motivated by previous mechanical enhancements for similar nanostitched laminates in ambient environments, hygrothermal effects on the 3D strengthening and toughening mechanisms of nanostitched laminates are investigated here for the first time, focusing on standard open-hole compression (OHC) testing of quasi-isotropic laminates. We report that the hygrothermal conditions of -55 degrees C/DRY and 100 degrees C/DRY correspond to ultimate strength increases of 2.6% and 5.9%, respectively, for nanostitched laminates over the baseline; and, room temperature/50% relative humidity (RT/50% RH) and 100 degrees C/wet conditions exhibit no change in ultimate strength, suggesting correlation of positive nanostitch effects with increased polymer brittleness. Subsequently, damage progression in step-wise interrupted OHC loading for selected hygrothermal conditions (RT/50% RH and 100 degrees C/DRY) was performed in coordination with high-resolution ex situ X-ray micro-computed tomography for various load steps up to 98% of failure load. No clear differences due to nanostitch in the damage progression are found up to 98% of ultimate strength, suggesting that the reinforcement effect is associated with interlaminar strength at ultimate load, and not preultimate damage. This study contributes first insights from high-resolution experimental mapping of nanostitched composite progressive damage subjected to hygrothermal conditions that may guide and inform mechanical enhancement approaches and improved progressive damage models. Future work is suggested to expand the environmental conditions considered, as well as visualize progressive damage nearer to failure to identify nanostitch effects on complex multimodal failure.

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This study demonstrates the mechanical, self‐sensing, and biological characteristics of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs)‐engineered 3D‐printed polyetheretherketone (PEEK) composite scaffolds, utilizing custom‐made feedstocks. Microstructural analysis and macroscale testing reveal that the PEEK/CNT scaffolds with 6 wt% CNT content and 46% relative density achieve a gauge factor of up to 75, a modulus of 0.64 GPa, and a compressive strength of 64 MPa. The PEEK/CNT2.5/GNP2.5 scaffolds evince still better performance, at a relative density of 73%, reporting a modulus of up to 1.1 GPa and a compressive strength of 122 MPa. Importantly, stability in mechanical and piezoresistive performance up to 500 cycles is noted, indicating a durable and reliable performance under cyclic loading. Murine preosteoblast cells (MC3T3‐E1) are used to biologically characterize sulfonated scaffolds over 14 days. Cytotoxicity, DNA, and alkaline phosphatase (ALP) levels are quantified through in vitro assays, evaluating cell viability, proliferation, and osteogenic properties. Notably, PEEK/CNT 6 wt% scaffolds exhibit nearly 80% cytocompatibility, while PEEK/CNT2.5/GNP2.5 scaffolds reach nearly 100%. Both types of scaffolds support cell differentiation, as evidenced by elevated ALP levels. These findings carry significant promise in bone tissue engineering, paving the way for the development of adaptive, intelligent structural implants boasting enhanced biocompatibility and self‐sensing capabilities.

In this study, CNT volume fraction, gas permeability, and electrical conductivity of horizontally aligned carbon nanotube (HACNT) nanocomposites were measured and analyzed according to the dilution ratio of epoxy and acetone and the applied pressure. The CNT volume fraction increased with decreasing dilution ratio and increasing pressure, indicating that the viscosity of the epoxy and pressure conditions play an important role in filling the gaps between the CNTs. Gas permeability decreases with increasing pressure, showing that higher pressure effectively improves gas barrier properties. As the dilution ratio decreased and the pressure increased, the electrical conductivity tended to increase, which can be interpreted because of strengthening the electrical connection between CNTs. This study provides important insights for various applications by suggesting the optimal dilution ratio and pressure conditions to achieve the highest performance of HACNT nanocomposites.

Manufacturing of aerospace-grade composite structures commonly utilizes autoclaves to provide convective heating for laminate curing, and pressure to remove voids from the laminates. However, autoclaves not only impose geometry constraints on the composite parts but can also lead to high capital and energy costs. To overcome these limitations, a novel manufacturing method has been developed that utilizes the high capillary pressure induced by various nanoporous network materials (NPNs) for void removal. By placing nanoporous network materials including vertically aligned carbon nanotubes (VA-CNTs), electro-spun polymer nanofibers (EPNs), and polymer aerogels (PAGs) at the ply-ply interfaces, manufacturing of void-free autoclave-grade aerospace carbon fiber reinforced plastic (CFRP) laminates have been demonstrated. In this work, we aim to investigate the void removal behavior enabled by NPN materials and establish correlations between various NPN materials' void removal capabilities and their characteristics including porosity, permeability, and achievable capillary pressure range. Experimental investigation of these characteristics was performed using a gas-liquid porometry for selected NPNs. A theoretical model informed by the experimentally measured NPN characteristics was developed to predict the infusion behavior of epoxy resin inside the NPNs at the interlaminar regions. In addition, an experimental setup was designed to enable in-situ observation of resin infusion and void evolution behaviors during the manufacturing process for aerospace-grade composite laminates using X-ray micro-computed tomography. Together, the modeling and the in-situ observation will provide more insights that will guide material selection and expand the options of NPN materials that can enable out-of-autoclave (OoA) manufacturing of aerospace-grade composite components.

Crystalline nanofibers, such as boron nitride (BNNTs) and carbon nanotubes (CNTs), are promising engineering materials due to their thermal, chemical and mechanical properties. BNNTs exhibit advantageous thermal properties and enhanced chemical stability, making them attractive for ceramic nanocomposite systems. In this study we developed preliminary synthesis and characterization methods for horizontally-aligned BNNT and CNTs nanocomposites for harsh (high-temperature) aerospace environments. Aligned BNNTs were synthesized using a scaffolded chemical vapor deposition (CVD) process, utilizing vertically-aligned CNTs (VA-CNTs) as templates. The resulting vertically-aligned BNNTs (VA-BNNT) were then processed using a bulk nanocomposite laminating (BNL) technique to achieve densification and horizontal alignment (HA). Microstructural characterization using scanning electron microscopy confirmed the alignment of the BNNTs, while x-ray diffraction and x-ray photoelectron spectroscopy analysis demonstrated the presence of crystalline hexagonal BN (h-BN) nanotubes with high chemical purity. Preliminary characterization of polymer composites with HA-CNT showed successful polymerization and negligible negative effects of nanotube reinforcement on polysiloxane resin curing behavior, a promising candidate for BNNT composites for high temperature applications. A single-ply HA-BNNT polymer composite with polycarbosilane resin was also fabricated for comparison. This work sets the foundation for further investigation into the properties and processing parameters of dense polymer and ceramic matrix BNNT composites.

Composite laminates utilizing autoclave-grade carbon fiber-reinforced plastic (CFRP) prepreg were manufactured using a polymer nanoporous network (NPN) interlayer that generates capillary pressure in lieu of pressure from an autoclave. The polymer nanofiber NPN film is integrated into the interlaminar region and is shown to eliminate voids in a vacuum-bag-only (VBO) curing process. After a preliminary investigation of the effect of NPN thickness on the interlaminar region and performance, an 8 μm thick polymer NPN was selected for a scaled manufacturing demonstration. Combining the polymer NPN with "out-of-oven" (OoO) electrothermal heating of a carbon nanotube (CNT)-heated tool, a 0.6 × 0.6 m void-free plate is successfully manufactured. OoO cure enables an accelerated cure cycle, which reduces the cure time by 35% compared to the manufacturer-recommended cure cycle (MRCC). X-ray microcomputed tomography (μ-CT) reveals that the laminates are void-free and of identical quality to autoclave-cured specimens. An array of mechanical tests including tension, compression, open-hole compression (OHC), tension-bearing (bolt-bearing), and compression after impact, reveal that the accelerated NPN-cured composites were broadly equivalent, with some instances of improved properties, relative to the autoclave-cured parts, e.g., OHC strength increased by 5%. With reduced capital costs, energy consumption, and increased throughput, the facile polymer NPN-enabled out-of-autoclave (OoA) fabrication method is shown to be a practical and attractive alternative to conventional autoclave fabrication.

Aerospace polysiloxane such as ultra high temperature resin (UHTR) has applications as ablative materials in thermal protection systems (TPS), specifically in the outermost layer of heat shields for re-entry space vehicles. For effective TPS use, the ablative material must possess specific characteristics, such as low density, low thermal conductivity, high temperature resistance, and the ability to form a stable and strong char. The aerospace industry employs fiber reinforced polymer composite materials due to their excellent strength-to-weight ratio in such cases. Crystalline nanofibers, such as carbon nanotubes (CNTs), offer remarkable properties like high specific strength, thermal stability, and tailorable electrical and thermal characteristics, making them potential advantageous reinforcement for UHTRs vs. traditional carbon (micro)fibers. However, current methods used for CNT-reinforced resins often yield nanocomposites with voids, randomly oriented and agglomerated CNTs, resulting in low packing density and limited property improvement. To overcome this challenge, a novel bulk nanocomposite laminating process (BNL) was utilized in this study. The BNL technique combines a facile CNT orientation and densification method during the resin polymer infiltration process. Through this approach, we successfully manufactured 6-ply CNT/polysiloxane laminates with aligned CNTs, uniform CNT distribution, and a substantial CNT packing fraction of 38 vol%. Various property characterization techniques, including micro-computed tomography (µCT), thermogravimetric analysis (TGA), and polarized Raman spectroscopy, were employed to investigate the properties of the CNT/polysiloxane laminates. The CNT/polysiloxane nanocomposite was cured to a carbon fiber-reinforced polysiloxane (CF/polysiloxane) composite and was tested in an oxyacetylene test bed (OTB) to evaluate its ablation properties.

Polymer-derived pyrolytic carbons (PyCs) are often desirable for low density high-temperature structural applications when they can be reinforced with high stiffness and strength fibers to address brittleness. Nanofibers, such as aligned carbon nanotubes (A-CNTs), can be an ideal reinforcement owing to their high mass-specific properties, and while modeling suggests that properties of A-CNTs at high volume fractions (i.e., 10-30 vol%) could yield significant enhancements, it is unknown how CNT confinement influences processing, as such materials have never been synthesized. Here, we report process development demonstrating the first successful fabrication of fully infused, void-free A-CNT carbon matrix nanocomposites (A/C-NCs) via polymer infiltration pyrolysis (PIP) that establishes a platform to study nanofiber-reinforced polymer-derived ceramics. The size of the average A/C-NC graphitic crystallites increases as CNT vol% increases up to 30 vol%, and the inter-layer separation of the PyC graphitic crystallites decreases, evidencing a nanoscale confinement effect observed in concert with increased mechanical performance. Vickers microhardness testing in the axial CNT direction of A/C-NCs shows agreement with prior data for low vol% CNTs in PyC and mechanical modeling, where specific hardness increases from -3.3 GPa/(g/cm3) for PyC to -6.7 GPa/(g/cm3) for 30 vol% A/C-NCs, demonstrating A/C-NCs as an advantaged superhard lightweight material.

A novel composite manufacturing technique, utilizing open nanoporous materials, termed Nano-Porous Network (NPN), are used to consolidate autoclave aerospace-grade epoxy prepreg carbon fiber reinforced composite (CFRP) laminates without an autoclave. The L-shape geometry parts were cured with vacuum-bag only (VBO) and shown to be void free. Previous studies have demonstrated that various NPNs, including an electrospun polymer nanofiber veil NPN as used here, can provide capillary forces that enhance resin flow at ply interfaces to enable void elimination without requiring autoclave pressure. In this study, a complex structure (i.e., L-shape) structure is manufactured with an electrospun polymer nanofiber veil between each unidirectional (UD) IM7/8552 ply and cured in a conventional oven under vacuum following the manufacturer-recommended cure cycle (MRCC) but not using autoclave pressure. The L-shape is studied extensively in the literature and is known to have a varying pressure distribution around the radius such that voids concentrate in the corner. The cured parts (baseline autoclave and NPN VBO processed) were inspected with X-ray micro-computed tomography (μCT) and shown to be void-free in both the flat regions and the curve and showed equivalent interlaminar strength to autoclave-cured parts, similar to previously reported flat panels. Exhibiting low capital cost, low energy consumption, and high manufacturing efficiency, this fabrication method has the potential to replace conventional autoclave fabrication in the aerospace industry.

Semiconductor packaging continues to reduce in thickness following the overall thinning of electronic devices such as smartphones and tablets. As the package becomes thinner, the warpage of the semiconductor package becomes more important due to the reduced bending stiffness and driven by thermal residual stresses and thermal expansion mismatch during the epoxy molding compound (EMC) curing to create the package. To address this packaging reliability issue, in this study, we developed a modified cure cycle that adds a rapid cooling step to the conventional cure cycle (CCC) to enhance the reliability of the EMC molded to a copper substrate (EMC/Cu bi-layer package) by lowering the bonding temperature of the EMC/Cu bi-layer package. Modeling of the package via Timoshenko theory including effective cure shrinkage allowed the rapid cooling step to be quantified and confirmed via experiments. The modified cure cycle resulted in a 26% reduction in residual strain, a 27% reduction in curvature, and a 40% increase in peel strength compared to the CCC, suggesting that this is an effective new method for managing warping effects in such packaged structures.

Semiconductor packaging based on an epoxy molding compound (EMC) currently has several disadvantages including warpage, limited processing area, and variability that all negatively affect cost and production yield. We propose a facile EMC molding process method using a flash electro-thermal carbon fiber heating (FE-CH) device based on carbon fiber-based papers to manufacture an EMC molded to a copper substrate (EMC/Cu bi-layer package) via Joule heating, and using this device, a modified cure cycle that combines the conventional cure cycle (CCC) with rapid cooling was performed using FE-CH to reduce the curvature of the EMC/Cu bi-layer package. Compared to the conventional hot press process, which uses 3.17 MW of power, the FE-CH process only uses 32.87 kW, resulting in a power consumption reduction of over 100 times when following the CCC. Furthermore, the FE-CH-cured EMC/Cu bi-layer package exhibits mechanical properties equivalent to those of a hot press-cured specimen, including the degree of cure, elastic modulus, curvature, bonding temperature, residual strain, and peel strength. The modified cure cycle using the FE-CH results in a 31% reduction in residual strain, a 32% reduction in curvature, and a 47% increase in peel strength compared to the CCC, indicating that this new process method is very promising for reducing a semiconductor package’s price by reducing the process cost and warpage.

Among natural fibers, basalt fibers have recently emerged as the main candidate to replace glass fibers in composite materials. Since the fiber/matrix interface strongly influences the final mechanical properties in a fiber reinforced composite, the current aim is to optimize the efficiency of the load transfer between the two different phases in the composite by growing carbon nanostructures (CNS), both nanofibers and nanotubes, on the surface of unsized basalt fibers exploiting less common catalysts compared to transition metals. Carbon nanostructures were grown onto unsized basalt fibers by chemical vapor deposition under different growth temperatures, using three different catalysts: copper, sodium, and iron. Considering the negative influence that high temperature has on the mechanical properties of basalt fibers, by lowering the synthesis temperature, we preserved the intrinsic properties of the basalt fibers, losing only 5% of the tensile strength at 300 degrees C growth temperature with a copper-based catalyst, while obtaining dense and uniform CNS growth. The different morphologies of the CNS obtained on the surface of the fibers were investigated by morphological and spectroscopic analyzes, while fiber/matrix adhesion was characterized by single fiber pull out tests, showing increases of 30% and 60% in interfacial shear strength and total pull out work, respectively. These less common catalysts provide an expanded design strategy for obtaining composites with improved interfacial bonding and multifunctional properties.