Saad Nauman

Simultaneous application of fibrous piezoresistive sensors for compression and traction detection in glass laminate composites.

This article describes further development of a novel Non Destructive Evaluation (NDE) approach described in one of our previous papers. Here these sensors have been used for the first time as a Piecewise Continuous System (PCS), which means that they are not only capable of following the deformation pattern but can also detect distinctive fracture events. In order to characterize the simultaneous compression and traction response of these sensors, multilayer glass laminate composite samples were prepared for 3-point bending tests. The laminate sample consisted of five layers of plain woven glass fabrics placed one over another. The sensors were placed at two strategic locations during the lay-up process so as to follow traction and compression separately. The reinforcements were then impregnated in epoxy resin and later subjected to 3-point bending tests. An appropriate data treatment and recording device has also been developed and used for simultaneous data acquisition from the two sensors. The results obtained, under standard testing conditions have shown that our textile fibrous sensors can not only be used for simultaneous detection of compression and traction in composite parts for on-line structural health monitoring but their sensitivity and carefully chosen location inside the composite ensures that each fracture event is indicated in real time by the output signal of the sensor.

Intelligent carbon fibre composite based on 3D-interlock woven reinforcement:

In this paper we describe the manufacturing and testing of an intelligent carbon fibre composite based on 3D-woven reinforcement. Piezoresistive fibrous sensors developed and optimized previously have been inserted into the carbon fibre reinforcement in the weft direction on a modified loom. These sensors were integrated at the top and bottom faces. Afterwards the reinforcement with embedded sensors was impregnated in epoxy resin using VARTM technology. The composite specimens thus obtained were tested for bending using the three-point bending test method. The results obtained show that the sensors allow simultaneous mapping of compression and traction at the top and bottom of the reinforcement when it undergoes bending. This is due to the fact that, unlike traditional strain gages, our sensors become integral part of the reinforcement and follow the tow architecture as dictated by the weaving process and interlacement pattern. Moreover, these sensors are compatible with the weaving process as they are flexible and sensitive enough to follow the deformation pattern of the reinforcement. Such sensors can be inserted inside various types of reinforcements during weaving in both warp and weft directions. Their location can be strategically chosen so as to form a network of sensors inside the reinforcement capable of following the deformation patterns of the reinforcement and mapping its stress–strain history.

Smart sensing layer for the detection of damage due to defects in a laminated composite structure

A smart sensing layer based on polystyrene and carbon nanoparticles has been developed. It has been deposited on the composite specimens for real-time, in situ monitoring of structural health. The strain response of the smart sensing layer has been recorded for composite laminates using different defect configurations (notch spacing). Numerical simulations of the stress–strain concentration have been carried out in order to determine the state of strain at the smart sensing layer, in the presence of different notch configurations. It has been observed that the sensing layer detects well the presence of large deformations and damage due to defects in the structure, with clearly defined peaks at the points of structural damage.

Liquid exfoliated graphene smart layer for structural health monitoring of composites

Graphene nanosheets were exfoliated from graphite using liquid exfoliation method. Smart sensing layer was prepared by dispersing graphene nanosheets in thermoplastic polyurethane. The smart sensing layers thus obtained were pasted on to the glass fiber laminated composite specimens. The sensing layer due to its piezoresistivity was employed for detecting strains in the composite specimens. The results show that the smart sensing layer can be employed for strain sensing in the composite structures. The results hold promise for various applications of these sensors for structural health monitoring in composite parts.

Transverse Shear Behavior of a Nomex Core for Sandwich Panels

The out-of-plane transverse shear characteristics of a Nomex honeycomb core have been studied. Finite-element analyses were performed to find the equivalent transverse shear moduli of the honeycomb core by using a unit-cell-based modeling approach with account of the orthotropic nature of Nomex paper. The results obtained are compared with those of three theoretical approaches. The differences between the numerical and theoretical results are attributed to the isotropic behavior of the basic core material considered in the theoretical approaches.

Geometrical modelling of orthogonal/layer-to-layer woven interlock carbon reinforcement

For the present work, we have studied the mesostructural geometry of orthogonal/layer-to-layer carbon–glass reinforcements woven on a conventional loom. The geometry of such woven reinforcements can be categorized in terms of crimp amplitude and cross-sectional shape of the warp and weft tows. These two vary with the structure of the woven fabric. The study was meant to characterize their geometry and study the influence of various factors on their mesostructural geometry. A geometrical modelling approach is developed and the results are compared with the geometrical parameters obtained from measurements on optical photomicrographs and the surface of the woven fabrics. It is demonstrated that the modelling approach can be used for the calculation of crimp values in 3D interlock structures.

Smart textiles for structural health monitoring of composite structures

Abstract Flexible polymers that incorporate conductive fillers can act as piezoresistive materials and are suitable for the design and fabrication of smart textile reinforcements for intelligent composites. Two applications based on coating of textile materials with carbon nanoparticles dispersed in polymer solutions for nondestructive evaluation (NDE) of glass laminate composites are presented. The first part presents a composite NDE system based on fibrous sensors. Polyethylene filaments coated with a sensing layer were placed inside textile reinforcements near top and bottom layers. After resin infusion, the resulting composite was subjected to bending tests. In the second part, a smart composite containing the sensing layer on the surface is presented. The strain response of the smart sensing layer has been recorded for composites with different defect configurations. The results proved that both variants of sensors are capable of detecting deformations and damage in composite structure.

Development of Flexible Cotton-Polystyrene Sensor for Application as Strain Gauge

A smart sensing thread based on a cotton substrate and coating realized from polystyrene and carbon nanoparticles has been developed. Manufacturing method used is an innovative extru-coating procedure developed especially for the purpose. The strain response of the smart sensing thread has been recorded. It has been observed that the sensing thread has a heterogeneous structure along the cross section. This is because of the fact that most of the coating material is deposited at the surface and the sub-surface layer. The core receives the least amount of absorbed solution. This has been confirmed by SEM image analysis and visual analysis of the fracture specimens as well. The dynamic range of the sensor was found to be 11%, while the sensitivity value was calculated to be 15.5. The smart sensing threads are able to detect strains as the electrical resistance changes with strain with a rather high gauge factor and can be used for various sensing applications as strain gauges and flexible sensors.