Lightweight primary and secondary structures of aircraft, wind turbines and automobile are mostly made of polymer-matrix composites. The selection of fibre reinforced polymer (FRP) composites for the primary structure is performance-based assuming defect-free components, especially in the aerospace industry. However, for the usage of FRP composites for secondary structures, the effect of manufacturing induced defects can be tolerated for cost-effective manufacturing. Fibre waviness has a major influence on the mechanical performance of composites and its study is one of the major concerns. The present work deals with an overview of the earlier reported studies on the effect of fibre waviness, and its formation, on the elastic properties and mechanical response of the FRP composites. Accumulation and discussion of results of the existing literature over the past two decades are summarized together up to the current status in the field. Capabilities of different non-destructive techniques used for characterisation of fibre waviness defect are summarized.

An Overview of The Formation of Fibre Waviness and Its Effect on The Mechanical Performance of Fibre Reinforced Polymer Composites

https://pureadmin.qub.ac.uk/ws/files/184228727/Sebaey_et_al_preprint.pdf

A microscale integrated approach to measure and model fibre misalignment in fibre-reinforced composites

Among a variety of defects associated with composite technology, fibre wrinkles are known to be a major source of failure for fibre reinforced plastic and closely associated with the ever popular automated fibre placement technique. In the present work, with the aim to investigate their influence on the failure of carbon fibre reinforced plastics (CFRP), composite laminates containing fibre wrinkles of varying architectures have been designed and prepared utilizing gaps and overlaps based on the understanding of wrinkle formation mechanisms. The effects of these engineered wrinkles with different combination of gaps and overlaps on the mechanical performance of CFRP were systematically investigated. A maximum of 21% and 37% drop in the tensile and compressive strength were recorded for the most severe combination of gaps and overlaps. A simple analytical model was proposed to relate the wrinkle angle to the defect characteristic parameters and a good agreement with experimental results was obtained. Furthermore, numerical simulations were conducted to inform the failure mechanisms where different wrinkle models were generated using previously developed pre-processing tools. Good agreements with experimental observations were obtained in terms of ply waviness, strength and failure modes. These findings provide certain practical insights for controlling defects in composite manufacturing processes.

Understanding the impact of fibre wrinkle architectures on composite laminates through tailored gaps and overlaps

Effect of tow gaps on impact strength of thin composite laminates made by Automated Fiber Placement: Experimental and semi-analytical approaches

Stiffness and buckling analysis of variable stiffness laminates including the effect of automated fibre placement defects

Effect of Gap Induced Waviness on Compressive Strength of Laminated Composites

Recent advances in material science and self-sensing technology have enabled the development of cement-based nanocomposite sensors that detect the damage on their own by exhibiting piezoelectric properties corresponding to the response of the structures. The present study involves the development and implementation of these sensors in the structural components and monitors the response by correlating the piezoelectric properties of the sensors with the stress-strain response to identify the potential damage. For this purpose, the carbon fiber (CF) and multiwalled carbon nanotubes (MWCNT) are used as nanofiller in the cementitious matrix to develop the self-sensing sensors. These sensors possess high strength, large elastic modulus, and piezo resistivity properties, which make them promising smart sensor materials for structural health monitoring applications. Two example applications involving the beam and column as the structural components are used for the experimentation. After embedding the sensors into the structural components, the response is evaluated in the form of resistance versus load. The self-sensing sensor is capable of detecting the nanostructural cracks during the loading of the system. Based on the severity of loading, the resistivity will indicate the damage state of the structural component which helps in deciding the suitable retrofitting strategies for the maintenance of the structural component to elongate the service life of the structures. The developed sensors also possess good mechanical and electrical properties and hence they have promising characteristics for real-time health monitoring applications.

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Development and Implementation of Cement-Based Nanocomposite Sensors for Structural Health Monitoring Applications: Laboratory Investigations and Way Forward

The authors would like to make the following corrections about the published paper [...]

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Correction: Roopa et al. Development and Implementation of Cement-Based Nanocomposite Sensors for Structural Health Monitoring Applications: Laboratory Investigations and Way Forward. Sustainability 2022, 14, 12452

There is an increased demand for cement nanocomposites in the twenty-first century due to their composition, higher strength, high efficiency, and multiscale nature. As carbon nanotubes (CNTs) possess extremely high strength, resilience, and stiffness, inclusion of carbon nanotubes in small quantities to the concrete mix makes them a multifunctional material. A molecular level understanding is significant to capacitate the macrolevel properties of these composites. In the proposed work, molecular dynamics (MD) simulations are used to understand the behaviour of the composites at the atomic level and continuum mechanics with representative volume element (RVE) homogenization modelling is carried out for interfacial interaction study of composites. The mechanical properties such as Young’s modulus, shear modulus, and poisons are evaluated using previous methods of simulations for different compositions of nanomaterials in cement matrix. The FORCITE module of MD simulation and square RVE model is used to determine the mechanical, electrical properties, and elastic constants of the cement nanocomposite. The MD simulation describes the linking effect of CNT into cement matric, and the RVE modelling study reveals the pull-out effect of CNT from matrix. From experimental and analytical studies, it is found that increase in CNT till 0.5% weight fraction increases the mechanical properties about 12% and further increasing of CNT weight fraction causes a reduction in mechanical properties about 5% due to the agglomeration of nanotubes. The density of states method in MD simulation indicates that mobility of the electrons increases with an increase in carbon nanotube proportion in the composites. The experimental test results substantiate the analytical studies, and the error obtained from both approaches is less than 20%. From the analytical study, the average maximum Young’s modulus, shear modulus, and bulk modulus are obtained as 46 GPa, 31 GPa, and 32 GPa for 0.5% weight fraction of CNT in cement matrix. Hence, it is concluded that 0.5% weight fraction of CNT is considered as optimum dosage to obtain better electrical and mechanical properties.

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A. Roopa

Papers

Effect of Gap Induced Waviness on Compressive Strength of Laminated Composites

Development and Implementation of Cement-Based Nanocomposite Sensors for Structural Health Monitoring Applications: Laboratory Investigations and Way Forward

Correction: Roopa et al. Development and Implementation of Cement-Based Nanocomposite Sensors for Structural Health Monitoring Applications: Laboratory Investigations and Way Forward. Sustainability 2022, 14, 12452

Study on Interfacial Interaction of Cement-Based Nanocomposite by Molecular Dynamic Analysis and an RVE Approach