Strain sensing efficiency of hierarchical nano-engineered smart twill-weave composites: Evaluations using multiscale numerical simulations

This paper evaluates the strain-sensing ability of a nanoengineered hierarchical twill weave composite using multiscale numerical simulations. Piezoresistivity is incorporated in such composite by introducing carbon nanotubes (CNT) in the polystyrene (PSS) matrix so as to form a percolating microstructure. The glass fiber twill weave, which itself contains CNT-modified PSS matrix inside the yarns, is coated with thin film of such piezoresistive matrix to obtain the smart composite configuration. The methodology, presented in this paper, captures the hierarchical intricacies at multiple length scales and implements various mechanical damage mechanisms at subsequent interactive length scales as well as consequent electrical responses so as to yield macroscopic electromechanical response. The simulated responses show excellent correlation with experimental observations signifying the efficacy of the simulation methodology. Such a detailed multiscale approach can provide valuable insights towards tuning of structural hierarchies at multiple length scales for efficient design of smart woven laminated composites

Spatial damage sensing ability of metallic particulate-reinforced cementitious composites: Insights from electrical resistance tomography

The paper evaluates the spatial damage sensing ability of self-sensing mortars containing up to 40% waste metallic iron powder by volume as cement-replacement. The spatial damage-sensing ability is evaluated using a framework that integrates the electrical resistance tomography (ERT)-based conductivity reconstruction algorithm with multiscale numerical homogenization with a view to enable microstructure-guided design of such self-sensing composites. The ERT-based framework uses experimentally measured boundary electrode voltages as input; assigns the effective conductivity of the composite (obtained from numerical homogenization) as initial estimate of the conductivity distribution and initiates the iterative process involving the well-posed forward model and the ill-posed inverse problem to obtain the conductivity map in the damaged configuration. The reconstructed damage maps, thus obtained, confirm sufficient spatial damage-sensing ability of mortars containing 30% or greater amount of iron powder validating the applicability of such self-sensing composites towards spatial damage sensing for health monitoring of structures

Fracture Response of Metallic Particulate-reinforced Cementitious Composites: Insights from Experiments and Multiscale Numerical Simulations

This paper presents an experimental and numerical investigation into the fracture response of mortars containing up to 30% waste iron powder by volume as OPC-replacement. The iron powder-modified mortars demonstrate significantly improved strength and fracture properties as compared to the control mortars due to presence of elongated iron particulates in the powder. With a view to develop a predictive tool towards materials design of such particulate-reinforced systems, fracture responses of iron powder-modified mortars are simulated using a multiscale numerical approach. The approach implements multi-scale numerical homogenization involving cohesive zone-based damage at the matrix-inclusion interface and isotropic damage in the matrix to obtain composite constitutive response and fracture energy. Consequently, these results serve as input to macro-scale XFEM-based three-point-bend simulations of notched mortar beams. The simulated macroscopic fracture behavior exhibit excellent match with the experimental results. Thus, the numerical approach links the material microstructure to macroscopic fracture parameters facilitating microstructure-guided material design

Microstructure-guided numerical simulation to evaluate the influence of phase change materials (PCMs) on the freeze-thaw response of concrete pavements

The use of phase change materials in infrastructure has gained significant attention in the recent years owing to their robust thermal performance. This study implements a numerical simulation framework using finite element analysis to evaluate the influence of phase change materials (PCMs) on the thermal response of concrete pavements in geographical regions with significant winter weather conditions. The analysis is carried out at different length scales. The latent-heat associated with different PCMs is efficiently incorporated into the simulation framework. Besides, the numerical simulation framework employs continuum damage mechanics to evaluate the influence of PCMs on the freeze-thaw induced damage in concretes. The simulations show significant reductions in the freeze-thaw induced damage when PCMs are incorporated in concrete. The numerical simulation framework, developed here, provides efficient means of optimizing the material design of such durable PCM-incorporated concretes for pavements by tailoring the composition and material microstructure to maximize performance

Influence of Microencapsulated Phase Change Materials (PCMs) on the Chloride Ion Diffusivity of Concretes Exposed to Freeze-thaw Cycles: Insights from Multiscale Numerical Simulations

Use of phase change materials (PCMs) to tailor the thermal performance of concretes by efficient energy storage and transmission has gained traction in recent years. This study incorporates microencapsulated PCMs as sand-replacement in concrete bridge decks and performs numerical simulation involving multiple interactive length scales to elucidate the influence of PCM-incorporation in concretes subjected to combined freeze-thaw and chloride ingress-induced deterioration. The simulations show significant increase in durability against combined freeze-thaw and chloride ingress-induced deterioration in concretes when microencapsulated PCMs are incorporated. In addition, a reliability-based probabilistic analysis shows significant increase in life expectancy of bridge decks with PCM-incorporation. The numerical approach presented here provides efficient means to develop design strategies to tune dosage and transition temperature of PCMs to maximize durability of concrete structures in regions that experience significant winter weather conditions

Influence of Microencapsulated Phase Change Materials (PCMs) on the Chloride Ion Diffusivity of Concretes Exposed to Freeze-thaw Cycles: Insights from Multiscale Numerical Simulations

Use of phase change materials (PCMs) to tailor the thermal performance of concretes by efficient energy storage and transmission has gained traction in recent years. This study incorporates microencapsulated PCMs as sand-replacement in concrete bridge decks and performs numerical simulation involving multiple interactive length scales to elucidate the influence of PCM-incorporation in concretes subjected to combined freeze-thaw and chloride ingress-induced deterioration. The simulations show significant increase in durability against combined freeze-thaw and chloride ingress-induced deterioration in concretes when microencapsulated PCMs are incorporated. In addition, a reliability-based probabilistic analysis shows significant increase in life expectancy of bridge decks with PCM-incorporation. The numerical approach presented here provides efficient means to develop design strategies to tune dosage and transition temperature of PCMs to maximize durability of concrete structures in regions that experience significant winter weather conditions

Finite Element-Based Numerical Simulations to Evaluate the Influence of Wollastonite Microfibers on the Dynamic Compressive Behavior of Cementitious Composites

This paper investigates the dynamic compressive behavior of wollastonite fiber-reinforced cementitious mortars using multiscale numerical simulations. The rate dependent behavior of the multiphase heterogeneous systems is captured in a multiscale framework that implements continuum damage towards effective property prediction. The influence of wollastonite fiber content (% by mass) as cement replacement on the dynamic compressive strength and energy absorption capacity is thereafter elucidated. An average compressive strength gain of 40% is obtained for mortars with 10% wollastonite fiber content as cement replacement, as compared to the control mortar at a strain rate of 200/s. The rate dependent constitutive responses enable the computation of energy absorption, which serves as a comparative measure for elucidating the material resistance to impact loads. Approximately a 45% increase in the dynamic energy absorption capacity is observed for the mixture containing 10% wollastonite fibers, as compared to the control case. Overall, the study establishes wollastonite fibers as a sustainable and dynamic performance-enhanced alternative for partial cement replacement. Moreover, the multiscale numerical simulation approach for performance prediction can provide an efficient means for the materials designers and engineers to optimize the size and dosage of wollastonite fibers for desired mechanical performance under dynamic loading conditions

Experimental and Numerical Investigation of the Fracture Behavior of Particle Reinforced Alkali Activated Slag Mortars

This paper presents fracture response of alkali-activated slag (AAS) mortars with up to 30% (by volume) of slag being replaced by waste iron powder which contains a significant fraction of elongated particles. The elongated iron particles act as micro-reinforcement and improve the crack resistance of AAS mortars by increasing the area of fracture process zone (FPZ). Increased area of FPZ signifies increased energy-dissipation which is reflected in the form of significant increase in the crack growth resistance as determined from R-curves. Fracture response of notched AAS mortar beams under three-point bending is simulated using extended finite element method (XFEM) to develop a tool for direct determination of fracture characteristics such as crack extension and fracture toughness in particulate-reinforced AAS mortars. Fracture response simulated using the XFEM based framework correlates well with experimental observations. The comprehensive fracture studies reported here provide an economical and sustainable means towards improving the ductility of AAS systems which are generally more brittle than their conventional ordinary portland cement counterparts.Comment: This article has been accepted for publication in ASCE's Journal of Materials in Civil Engineerin

Microstructure and Strength Development of Sodium Carbonate–Activated Blast Furnace Slags

This paper presents the study of alkali-activated slags where sodium carbonate acts as a primary activator. The slow activation mechanism of sodium carbonate is accelerated by sodium hydroxide and with traces of calcium hydroxide. Strength development and the progress of hydration of the mixes were studied with the phase transformation and development of microstructural features through quantitative techniques such as thermogravimetric analysis and phase-identification techniques such as Fourier transform infrared spectroscopy and X-ray diffraction. Sodium carbonate replacement with sodium hydroxide and the presence of calcium hydroxide in the binder as a replacement for the slag enhances the rate of dissolution of slag, leading to faster strength development. Calcium hydroxide significantly increases the compressive strength, even at an early age. On the other hand, sodium hydroxide substitution is effective at later ages of the reaction when used at high dosages (e.g., 40%). Formation of strength-giving phases such as hydrotalcite and calcium aluminum silicate hydrate are confirmed with microstructure analysis and explain the strength development

Experimental and Numerical Investigation of the Fracture Behavior of Particle Reinforced Alkali Activated Slag Mortars

This paper presents fracture response of alkali-activated slag (AAS) mortars with up to 30% (by volume) of slag being replaced by waste iron powder which contains a significant fraction of elongated particles. The elongated iron particles act as micro-reinforcement and improve the crack resistance of AAS mortars by increasing the area of fracture process zone (FPZ). Increased area of FPZ signifies increased energy-dissipation which is reflected in the form of significant increase in the crack growth resistance as determined from R-curves. Fracture response of notched AAS mortar beams under three-point bending is simulated using extended finite element method (XFEM) to develop a tool for direct determination of fracture characteristics such as crack extension and fracture toughness in particulate-reinforced AAS mortars. Fracture response simulated using the XFEM based framework correlates well with experimental observations. The comprehensive fracture studies reported here provide an economical and sustainable means towards improving the ductility of AAS systems which are generally more brittle than their conventional ordinary portland cement counterparts