Irina Cristian

Online Measurement of Structural Deformations in Composites

This paper describes a new approach of Nondestructive Evaluation (NDE) using fibrous sensors inserted inside composite reinforcements during their weaving. A flexible piezoresistive fibrous sensor has been developed and optimized for in situ structural deformation sensing in carbon composites. The sensor was inserted, in the weft direction, in three-dimensional warp interlock reinforcement during the weaving process on a special weaving loom. The reinforcement was then impregnated in epoxy resin and was later subjected to quasi-static tensile strain. It was found that the sensor was able to detect deformations in the composite structure until rupture since it was inserted together with reinforcing tows. The morphological and electromechanical properties of the fibrous sensors have been analyzed using scanning electron microscopy, tomography and yarn tensile strength tester. An appropriate data treatment and recording device has also been developed and utilized. The results obtained for carbon composite specimens under standard testing conditions (NF EN ISO 527-4 Plastiques, CEN, 1997) have validated in situ monitoring concept using our textile fibrous sensors.

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.

A Study of Strength Transfer from tow to Textile Composite Using Different Reinforcement Architectures

The paper proposes an experimental and analytical approach of designing composites with the predetermined ultimate strength, reinforced with warp interlock fabrics. In order to better understand the phenomena of transfer of tensile properties from a tow to the composite, intermediate phases of composite manufacturing have also been taken into account and tensile properties of tows taken from the loom and the woven reinforcements have also been tested. Process of transfer of mechanical properties of raw materials to the final product (composite) depends on various structural factors. Here the influence of weave structure, which ultimately influences crimp has been studied. A strength transfer coefficient has been proposed which helps in estimating the influence of architectural parameters on 3D woven composites. 3 woven interlock reinforcements were woven to form composites. The coefficients of strength transfer were calculated for these three variants. The structural parameters were kept the same for these three reinforcements except for the weave structure. In was found that the phenomenon of strength transfer from tow to composite is negatively influenced by the crimp. In general the strength transfer coefficients have higher values for dry reinforcements and afterwards due to resin impregnation the values drop.

A study on the beam pattern of ultrasonic sensor integrated to textile structure

Purpose – During the past decades, several researchers have introduced devices that use sonar systems to detect and/or to determine the object location or to measure the distance to an object using reflected sound waves. The purpose of this paper is to use sonar sensor with textile structure and to test it for detection of objects.Design/methodology/approach – In this study, a sonar system based on intelligent textiles approach for detection of objects has been developed. In order to do this, ultrasonic sensor has been integrated to textile structures by using conductive yarns. Furthermore, an electronic circuit has been designed; PIC 16F877 microcontroller unit has been used to convert the measured signal to meaningful data and to assess the data. The algorithm enabling the objects detection has also been developed. Finally, smart textile structure integrated with ultrasonic sensor has been tested for detection of objects.Findings – Beam shape is presented related to identified object and compared with t...

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.

Geometrical modelling of angle warp interlock fabrics

A geometrical modelling approach has been developed which predicts all the necessary geometrical parameters for multilayer angle warp interlock weaves. The model requires tow and weaver data as input and gives fabric thickness, warp and weft crimp angle, areal weight and fibre volume fraction (FVF) as outputs. In order to validate the model we have woven three angle warp interlock woven reinforcements, having same number of total layers, on a conventional loom, using carbon multifilament tows in warp and glass multifilament tows in weft. The depth of the binder (maximum number of layers traversed by the binding warp in vertical plane) was maximum for the first variant (5). The binder tow traversed all the five layers so that this variant is termed as through-the-thickness angle interlock. For the second variant it was reduced to an intermediate level (3), whereas for the third one it was minimum (2) so as to conceive a layer-to-layer interlock structure. The geometry of such woven reinforcements can be categorised 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 and weaving parameters, ultimately influencing the areal weight, size of the unit cell and FVF of the fabric reinforcement. Results obtained show that the modelling approach can be successfully applied to calculate necessary fabric geometry parameters from minimum number of manufacturer and weaver data.

Development of comfortable and well-fitted bra pattern for customized female soft body armor through 3D design process of adaptive bust on virtual mannequin

Abstract The performance of various protective clothing i.e., soft body armor depends mainly on material type, fabric construction and garment design. However, most female soft body armor has been designed using traditional methods which face poor ballistic protection, less fitness and comfort. These problems mainly arise from corset problem due to using current inaccurate traditional bra sizing system which considers only cup size as a description of complex three dimensional (3D) breast volumes. Besides, female body armor manufacturing using this method enforced to involve different darts to accommodate the natural curvature of the female body, i.e. bust area. This brought the weak parts at the seams while ballistic impact and revealed discomfort due to accumulated fabrics at this area. The current study introduces a novel designing technique for developing female adaptive bust volume on 3D female virtual mannequin. The adaptive bust later used to generate different volumes of breast based on parametrization. The main purpose of our approach is to solve previous design problems by using the computer-aided design (CAD) knowledge in the morphological evolution of the chest and introduced it into a 3D design process for achievement of comfortable and well fitted 3D bra design. During 3D digitized modeling process, various cutting planes in x and y-direction from the bust origin have been intersecting with the bust at several angles. This intersection would help to extract the real surface of the body contour and creates the wireframe mesh on the bust. This wireframe mesh ensued different feature points on 3D expandable bust for defining the different volumes of breast based on their cup sizes. Moreover, 3D bra pattern is developed using the adaptive volume to validate the specific obtained volume. The flattened 2D patterns from the 3D model were also compared to the corresponding traditional 2D pattern. The result indicated that the proposed method is easier to implement and can generate 2D bra patterns with satisfactory fit and comfort. This is due to the 3D pattern derived from the new method which perfectly follows the exact body contours than assuming the measurement, as done into classical 2D graphical method. The study later associates different bust cups with the front part of female body armor panel to determine the possible variation for better performance and optimal comfort. In general, this approach solves previous design problems and helps to customize bra pattern and female body armor front panel patterns using CAD knowledge in the morphological evolution of the female bust volume. Further study is required to develop seamless female front body pattern in association with the respective bust volume. This will help to customize the ballistic vest which attains the required bust volume without involving dart for better comfort, ballistic protection and fitness.

Introduction to waterproof and water repellent textiles

Waterproof materials have an extraordinarily high use, with products for everyday clothing, sportswear and protective clothing for industrial or technical applications. The chapter begins with a review of the specific requirements imposed by the use of waterproofing and water repellent textile materials, on the assumption that waterproofing as a dominant function must harmonize with other functions by providing multifunctional products to the end user. Examples of this are breathable materials designed to create clothing that simultaneously provide waterproofing and wearing comfort. To fully understand how to make waterproof and water repellent materials, it is essential to have knowledge of textiles and clothing products and their behaviour in relation with the humidity, liquid and vapours. A key issue addressed in the chapter refers to technologies and methods for development of waterproof and water repellent textile materials, with emphasis on materials coated with polymers and those with surface treatments (plasma treatments, hybrid finishing, nano-coating, etc.).