@article{guha_berkowitz_grace_2024, title={A coupled approach of spatial dielectric mapping and unsupervised machine learning for damage detection and severity segmentation in polymer matrix composites}, volume={145}, ISSN={["1879-1174"]}, DOI={10.1016/j.ndteint.2024.103137}, journal={NDT & E INTERNATIONAL}, author={Guha, Rishabh D. and Berkowitz, Katherine and Grace, Landon R.}, year={2024}, month={Jul} }
 @article{berkowitz_guha_oluwajire_grace_2024, title={Verification and validation of dielectric mapping technique for non-destructive evaluation of polymer matrix composites}, ISSN={["1548-0569"]}, DOI={10.1002/pc.28848}, abstractNote={Abstract The rapid increase in use of polymer matrix composites in different industries underscores the need for reliable non‐destructive evaluation techniques to characterize small‐scale damage and prevent structural failure. A novel dielectric technique exploits moisture‐polymer interactions to identify and track damage, leveraging differences in dielectric properties between free and bound water. This technique has demonstrated the ability to detect low levels of damage, but the localization accuracy has not yet been evaluated. This work utilizes unsupervised machine learning to assess the technique's ability to identify the damage boundary following a low‐velocity impact event. Bismaleimide/quartz and E‐glass/epoxy laminates were impacted via drop tower to induce varying levels of damage, and subsequently inspected via dielectric technique at several moisture levels by weight. Resulting data was processed via k‐means clustering and the identified damage boundary was compared to a boundary obtained from backlit images and scanning electron microscopy. Accuracy was quantified using developed metrics for damage centroid and boundary identification. The technique averaged 93.9% accuracy in determining the damage center and 77.5% accuracy in identifying the damage boundary. Results indicated the technique's effectiveness across varying moisture levels, particularly in damage centroid identification. Localization accuracy was shown to be insensitive to moisture content, improving the technique's practical capabilities. Further analysis revealed potential for delineation of delaminations. Highlights Low‐velocity impact of two material architectures. Damage boundary determined and validated via scanning electron microscopy. Detected damage site via dielectric technique compared to damage boundary. High technique accuracy revealed; >90% centroid localization accuracy. Potential for delamination delineation observed.}, journal={POLYMER COMPOSITES}, author={Berkowitz, Katherine and Guha, Rishabh D. and Oluwajire, Oluwatimilehin and Grace, Landon R.}, year={2024}, month={Aug} }
 @article{guha_danilov_berkowitz_oluwajire_grace_2023, title={Consequences of Humidity Cycling on the Moisture Absorption Characteristics of Epoxy Resins with Different Network Architectures}, volume={1}, ISSN={["2637-6105"]}, url={https://doi.org/10.1021/acsapm.2c01570}, DOI={10.1021/acsapm.2c01570}, abstractNote={Absorbed moisture is a perpetual contributor to the steady loss of performance for in-service epoxy-based polymer materials. On the atomistic scale, the state of individual water molecules in a crosslinked epoxy is dependent on the strength of the secondary bonding interactions they engage in and their local physical environment. However, these chemical and physical variables can be tailored on the macroscopic scale through changes in the experimental curing schedule. In this study, crosslinked epoxy matrices with different network architectures were cured by varying the stoichiometric mixing ratios of the epoxy: hardener combination. The samples were subsequently subjected to fluctuating humidity conditions which comprises repeating cycles of high (∼95% RH) and ambient humidity. Both infrared (IR) spectroscopy and dielectric readings were successful in establishing a strong correlation between moisture absorption, network morphology, and dielectric properties. An anomalous behavior observed during the spectral peak analysis helped us understand how absorption history can redistribute the concentrations of water species at the same moisture concentrations. The results from this study elucidate how the phenomenon of absorption itself can act as a damage initiation event, and they also indicate that the spatial quantification of the different water species across a sample can allow us to map damage sites, nanopores, and areas with an overall higher void content.}, journal={ACS APPLIED POLYMER MATERIALS}, author={Guha, Rishabh D. and Danilov, Evgeny O. and Berkowitz, Katherine and Oluwajire, Oluwatimilehin and Grace, Landon R.}, year={2023}, month={Jan} }
 @article{guha_danilov_berkowitz_oluwajire_grace_2023, title={Suppressing Hydrogen Evolution in Aqueous Lithium-Ion Batteries with Double-Site Hydrogen Bonding}, volume={5}, ISSN={["2637-6105"]}, DOI={10.1021/acsapm.2c01570400}, number={1}, journal={ACS APPLIED POLYMER MATERIALS}, author={Guha, Rishabh D. and Danilov, Evgeny O. and Berkowitz, Katherine and Oluwajire, Oluwatimilehin and Grace, Landon R.}, year={2023}, month={Jan}, pages={400–411} }
 @article{idolor_berkowitz_guha_grace_2022, title={Nondestructive examination of polymer composites by analysis of polymer-water interactions and damage-dependent hysteresis}, volume={287}, ISSN={["1879-1085"]}, DOI={10.1016/j.compstruct.2022.115377}, abstractNote={Polymer composites are currently replacing metals in applications requiring design flexibility, high strength-to-weight ratio, and corrosion resistance. However, the damage modes in these materials are very different from metals and require specialized techniques to detect internal flaws which may exist even in the absence of visible surface damage. This study proposes a technique for damage detection in polymer composites which uses naturally absorbed moisture as an ‘imaging’ agent. The locally higher concentration of water in the ‘free’ state at damaged regions and the tendency of such water to quickly migrate to and from damage sites—exhibiting damage-dependent hysteresis—is leveraged for damage detection. To identify damaged regions, a machine learning approach is adopted using logistic regression to classify local regions as ‘undamaged’ or ‘damaged’. New possibilities resulting from higher sensitivity levels achievable by damage-dependent hysteresis are highlighted, providing a pathway to field deployment of the novel damage detection technique.}, journal={COMPOSITE STRUCTURES}, author={Idolor, Ogheneovo and Berkowitz, Katherine and Guha, Rishabh Debraj and Grace, Landon}, year={2022}, month={May} }
 @article{guha_rahmani_berkowitz_pasquinelli_grace_2022, title={Temporal evolution of the behavior of absorbed moisture in a damaged polymer-quartz composite: A molecular dynamics study}, volume={214}, ISSN={["1879-0801"]}, DOI={10.1016/j.commatsci.2022.111690}, abstractNote={• Interfacial Debonding was simulated on a nanoscale using an atomistic model of a quartz-fiber composite. • The temporal behavior of absorbed moisture was analyzed near the damage site. • Irrespective of the initial state of moisture in the composite, they eventually agglomerate near the damage location. • Spatial confinement near the interface bolsters previous experiments which hypothesize that absorbed moisture behaves like bulk water when clustered at microcracks. Exposure of a composite structure to mechanical or environmental stressors often leads to the formation of damage sites which contain rupture mechanisms such as matrix cracking and interfacial debonding. Continued accumulation of this type of small-scale damage can cause sudden and catastrophic large-scale failure. A novel damage characterization technique which leverages the altered physical and chemical states of naturally absorbed moisture in response to sub-micron scale damage has recently shown promise for early detection of damage. In this work, molecular dynamics simulations are used to better understand the differences in the behavior of absorbed water molecules near a damage site. The results show that, irrespective of the initial distribution of molecular water throughout the composite, or the presence of polar atoms in the polymer matrix, water tends to preferentially cluster near the damage location. It was also found that spatial confinement near the polymer-fiber interface hinders diffusion of the water molecules into the polymer matrix. These molecular level insights bolster the hypothesis formulated in previous experimental studies that absorbed moisture behaves like free water in terms of its dielectric activity when the water molecules agglomerate at the damage location. Consequently, this locally distinct permittivity can be leveraged for damage detection and quantification.}, journal={COMPUTATIONAL MATERIALS SCIENCE}, author={Guha, Rishabh D. and Rahmani, Farzin and Berkowitz, Katherine and Pasquinelli, Melissa and Grace, Landon R.}, year={2022}, month={Nov} }
 @article{idolor_guha_berkowitz_grace_2021, title={An experimental study of the dynamic molecular state of transient moisture in damaged polymer composites}, volume={42}, ISSN={["1548-0569"]}, url={https://doi.org/10.1002/pc.26066}, DOI={10.1002/pc.26066}, abstractNote={AbstractPolymeric composites absorb measurable amounts of moisture from their environment in almost all operating conditions. This absorbed moisture exists either in the “free” state, without any interactions, or in the “bound” state—interacting with the polymer matrix via secondary bonding mechanisms. The ratio and distribution of these water states within a moisture‐contaminated polymer composite are sensitive to physical damage. However, the water state distribution is also affected by variations in total water content resulting from humidity or precipitation‐driven fluctuations in the ambient environment, which could confound the ability to detect damage within the polymer matrix using this technique. To understand the effect of moisture content variations on water state distribution, low levels of barely visible impact damage were induced in epoxy/glass fiber composites. Spatial variations in polymer–water interactions were identified by their characteristic dielectric properties, measured using a split post dielectric resonator operating at 5 GHz. Gravimetric moisture uptake and relative permittivity were monitored during the absorption and desorption processes. Results indicate moisture absorption/desorption history has a significant effect on the sensitivity of damage detection using water state variations. Damage‐dependent hysteresis was observed in relative permittivity, highlighting an avenue by which the confounding effects of moisture absorption/desorption history may be mitigated.}, number={7}, journal={POLYMER COMPOSITES}, publisher={Wiley}, author={Idolor, Ogheneovo and Guha, Rishabh Debraj and Berkowitz, Katherine and Grace, Landon}, year={2021}, month={Jul}, pages={3391–3403} }
 @article{guha_idolor_berkowitz_pasquinelli_grace_2021, title={Exploring secondary interactions and the role of temperature in moisture-contaminated polymer networks through molecular simulations}, volume={17}, ISSN={["1744-6848"]}, url={https://doi.org/10.1039/D0SM02009E}, DOI={10.1039/d0sm02009e}, abstractNote={We investigated the effect of temperature variation on the secondary bonding interactions between absorbed moisture and epoxies with different morphologies using molecular dynamics simulations.}, number={10}, journal={SOFT MATTER}, publisher={Royal Society of Chemistry (RSC)}, author={Guha, Rishabh D. and Idolor, Ogheneovo and Berkowitz, Katherine and Pasquinelli, Melissa and Grace, Landon R.}, year={2021}, month={Mar}, pages={2942–2956} }
 @article{guha_idolor_berkowitz_pasquinelli_grace_2021, title={Exploring secondary interactions and the role of temperature in moisture-contaminated polymer networks through molecular simulations (vol 17, pg 2942, 2021)}, volume={5}, ISSN={["1744-6848"]}, DOI={10.1039/d1sm90100a}, abstractNote={Correction for ‘Exploring secondary interactions and the role of temperature in moisture-contaminated polymer networks through molecular simulations’ by Rishabh D. Guha et al., Soft Matter, 2021, 17, 2942–2956, DOI: 10.1039/D0SM02009E.}, journal={SOFT MATTER}, author={Guha, Rishabh D. and Idolor, Ogheneovo and Berkowitz, Katherine and Pasquinelli, Melissa and Grace, Landon R.}, year={2021}, month={May} }
 @article{idolor_guha_berkowitz_geiger_davenport_grace_2021, title={Polymer-water interactions and damage detection in polymer matrix composites}, volume={211}, ISSN={["1879-1069"]}, url={https://doi.org/10.1016/j.compositesb.2021.108637}, DOI={10.1016/j.compositesb.2021.108637}, abstractNote={Polymer matrix composites have a tendency to absorb measurable moisture in nearly all operating environments. This absorbed moisture either becomes bound to the polymer network via secondary bonding interactions or exists as free water with negligible interactions. Damage creates new internal free volume where water molecules can exist in the latter state. This study introduces a novel basis for non-destructive examination in polymer matrix composites which leverages locally-higher concentration of free water in damaged areas. Experiments involved impact-induced sub-surface damage in a laminate prior to moisture exposure. Polymer-water interaction—determining the free or bound state of water—was characterized by near-infrared spectroscopy and microwave-range relative permittivity. Results show a direct correlation between the extent of local damage and higher relative levels of free water at damage sites.}, journal={COMPOSITES PART B-ENGINEERING}, publisher={Elsevier BV}, author={Idolor, Ogheneovo and Guha, Rishabh Debraj and Berkowitz, Katherine and Geiger, Carl and Davenport, Matthew and Grace, Landon}, year={2021}, month={Apr} }
 @article{guha_idolor_grace_2020, title={An atomistic simulation study investigating the effect of varying network structure and polarity in a moisture contaminated epoxy network}, volume={179}, ISSN={["1879-0801"]}, DOI={10.1016/j.commatsci.2020.109683}, abstractNote={Absorbed moisture is a frequent contributor to performance loss in polymer-based composite structures operating in nearly all environments. However, the fundamental mechanisms that govern water-polymer interaction remain poorly understood. In this molecular dynamics study, the polarity and internal structure of an epoxy-based composite matrix was varied through manipulation of crosslink density. A commonly used epoxy-hardener combination (DGEBA- DETA) was chosen and four different models were created with crosslinking density of 20%, 51%, 65% and 81% respectively. The results indicate that the increase in crosslinking leads to a greater availability of polar sites with a concomitant rise in available free volume. The rise in network polarity aids the hydrogen bonding interactions between the absorbed water and the composite matrix, but the greater availability of free volume also allows water molecules to cluster together through mutual hydrogen bonding activity. This results in a subsequent decrease in moisture interaction with polar sites at very high crosslink densities. It was also found that the diffusivity and average dipole moment of the absorbed moisture are correlated with the state of water molecules and that a greater percentage of network-bonded molecules tends to lower both of these quantities. These results are consistent with previously published experimental results which have contemplated the dual nature of water molecules in an epoxy network. The results also highlight the potential of leveraging this phenomenon for non-destructive inspection of the physical and chemical state of a polymer network.}, journal={COMPUTATIONAL MATERIALS SCIENCE}, author={Guha, Rishabh Debraj and Idolor, Ogheneovo and Grace, Landon}, year={2020}, month={Jun} }