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1. Laser induced graphene in fiberglass-reinforced composites for strain and damage sensing

   https://doi.org/10.1016/j.compscitech.2020.108367  

   Groo, Lori Anne ; Nasser, Jalal ; Zhang, Lisha ; Steinke, Kelsey ; Inman, Daniel ; Sodano, Henry Angelo ( October 2020 , Composites science and technology)

   null (Ed.)

   Structural health monitoring of fiber-reinforced composite materials is of critical importance due to their use in challenging structural applications where low density is required and the designs typically use a low factor of safety. In order to reduce the need for external sensors to monitor composite structures, recent attention has turned to multifunctional materials with integrated sensing capabilities. This work use laser induced graphene (LIG) to create multifunctional structure with embedded piezoresistivity for the simultaneous and in-situ monitoring of both strain and damage in fiberglass-reinforced composites. The LIG layers are integrated during the fabrication process through transfer printing to the surface of the prepreg before being laid up into the ply stack, and are thus located in the interlaminar region of the fiberglass-reinforced composite. The methods used in this work are simple and require no treatment or modification to the commercial fiberglass prepreg prior to LIG transfer printing which is promising for industrial scale use. The performance of the piezoresistive interlayer in monitoring both strain and damage in-situ are demonstrated via three-point bend and tensile testing. Additionally, the interlaminar properties of the fiberglass composites were observed to be largely maintained with the LIG present in the interlaminar region of the composite, while the damping properties were found to be improved. This work therefore introduces a novel multifunctional material with high damping and fully integrated sensing capabilities through a cost-effective and scalable process. 

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2. Fatigue damage tracking and life prediction of fiberglass composites using a laser induced graphene interlayer

   https://doi.org/https://doi.org/10.1016/j.compositesb.2021.108935  

   Groo, Lori Anne ; Nasser, Jalal ; Inman, Daniel ; Sodano, Henry ( August 2021 , Composites)

   null (Ed.)

   Fiberglass-reinforced composite materials are commonly used in engineering structures subjected to dynamic loading, such as wind turbine blades, automobiles, and aircraft, where they experience a wide range of unpredictable operating conditions. The ability to monitor these structures while in operation and predict their remaining structural life without requiring their removal from service has the potential to drastically reduce maintenance costs and improve reliability. This work exploits piezoresistive laser induced graphene (LIG) integrated into fiberglass-reinforced composites for in-situ fatigue damage monitoring and lifespan prediction. The LIG is integrated within fiberglass composites using a transfer-printing process that is scalable with the potential for automation, thus reducing barriers for widespread application. The addition of the conductive LIG within the traditionally insulating fiberglass composites enables direct in-situ damage monitoring through simple passive resistance measurements during tension-tension fatigue loading. The accumulation and propagation of structural damage are detected throughout the fatigue life of the composite through changes to the electrical resistance measurements, and the measurement trends are further used to predict the onset of catastrophic composite failure. Thus, this work results in a scalable and multifunctional composite material with self-sensing capabilities for potential use in high-performing, dynamic, and flexible composite structures. 

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3. Damage localization in fiberglass-reinforced composites using laser induced graphene

   https://doi.org/https://doi.org/10.1088/1361-665X/abdc0c  

   Groo, Lori Anne ; Nasser, Jalal ; Inman, Daniel ; Sodano, Henry ( February 2021 , Smart materials and structures)

   null (Ed.)

   Current in situ piezoresistive damage detection techniques for fiberglass-reinforced composites are limited in widespread application as they require complex processing techniques which inhibit the scalability of the methods. To eradicate such challenges and expand the use of piezoresistive monitoring of fiberglass composites, this work utilizes a simple, scalable process to coat electrically insulating commercial fiberglass prepreg with piezoresistive laser induced graphene (LIG) for the detection and localization of damage. Recently, LIG has attracted substantial research attention due to the simplicity of the methodology and the piezoresistance of the LIG. Here, the LIG is transfer printed onto commercial fiberglass prepreg which is subsequently used to localize damage in all three dimensions of the resultant fiberglass-reinforced composites while also maintaining the structural properties of the composites. A combination of in situ and ex-situ resistance measurements are used to accomplish this objective: First, in situ measurements are used to determine the relative location of damage in one-dimension under tensile loading. Subsequently, separate in situ measurements are used to locate damage through the thickness under flexural loading. Finally, ex-situ methods are used to calculate the two-dimensional location of a hole in a plate. The LIG is found to reliably and accurately localize the damage to the composite in each case thus demonstrating for the first time that transfer printed LIG enables self-sensing of damage location in fiberglass composites. The result of this work is thus a multifunctional material capable of locating damage in all three-dimensions which is notably fabricated using commercial materials and scalable methodology. 

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4. Transfer printed laser induced graphene strain gauges for embedded sensing in fiberglass composites

   https://doi.org/https://doi.org/10.1016/j.compositesb.2021.108932  

   Groo, Lori Anne ; Nasser, Jalal ; Inman, Daniel ; Sodano, Henry ( August 2021 , Composites)

   null (Ed.)

   The continuous monitoring of strain in fiber-reinforced composites while in service typically requires bonding a network of sensors to the surface of the composite structure. To eliminate such needs, and to reduce bulk and limit additional weight, this work utilizes the transfer printing of laser induced graphene (LIG) strain gauges onto the surface of commercial fiberglass prepreg for the in situ self-sensing of strain. The resultant embedded strain sensor is entirely integrated within the final composite material, therefore reducing weight and eliminating limitations due to external bonding compared to current alternatives. Additionally, the simple printing process used here allows for the customization of the size and sensing requirements for various applications. The LIG strain sensor is shown to be capable of tracking monotonic cyclic strain as shown during tensile loading and unloading of the host composite, while also proving capable of tracking the dynamic motion of the composite which is characterized via frequency response and sinusoidal base excitation. The LIG strain gauge in this work can thus be used for tracking either quasi-static or dynamic variations in strain for the determination of the deformation experienced by the material, as well as the frequency content of the material for structural health monitoring purposes. 

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5. Transfer Printed Laser Induced Graphene Strain Gauges for Embedded Sensing in Fiberglass Composites

   Groo, L. ; Sodano, H.A ( August 2021 , Composites)

   null (Ed.)

   The continuous monitoring of strain in fiber-reinforced composites while in service typically requires bonding a network of sensors to the surface of the composite structure. To eliminate such needs, and to reduce bulk and limit additional weight, this work utilizes the transfer printing of laser induced graphene (LIG) strain gauges onto the surface of commercial fiberglass prepreg for the in situ self-sensing of strain. The resultant embedded strain sensor is entirely integrated within the final composite material, therefore reducing weight and eliminating limitations due to external bonding compared to current alternatives. Additionally, the simple printing process used here allows for the customization of the size and sensing requirements for various applications. The LIG strain sensor is shown to be capable of tracking monotonic cyclic strain as shown during tensile loading and unloading of the host composite, while also proving capable of tracking the dynamic motion of the composite which is characterized via frequency response and sinusoidal base excitation. The LIG strain gauge in this work can thus be used for tracking either quasi-static or dynamic variations in strain for the determination of the deformation experienced by the material, as well as the frequency content of the material for structural health monitoring purposes. 

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