Capacitance measurements on integrated conductors for detection of matrix cracks in GFRP

Abstract

For the reliable and cost-efficient application of glass fibre polymer composites in structural applications, knowledge of the damage state of the material during operation is necessary. Within this work, a structural health monitoring method based on in-situ electrical capacitance measurements is presented, which enables damage monitoring in glass fibre reinforced polymers. For this purpose, individual glass fibre rovings in a non-crimp fabric were replaced by carbon fibre rovings at regular intervals. Additionally, specimens with solid or stranded copper conductors were manufactured to gain insights into the influences of conductor material and composition. The modified fabrics were implemented as 90∘ layers of [0/904]s glass fibre polymer cross-ply laminates. To monitor the progressive damage, conductive rovings were contacted, forming the capacitor walls of interleaved capacitors. Carbon fibre conductors show higher sensitivity of the capacitance to crack formation than solid or stranded copper conductors. Capacitance decrease measured in-situ during tensile tests on specimens with carbon fibre conductors shows a high correlation with crack initiation, further crack formation and speed of crack evolution. An analytical model can describe the correlation based on the assumptions of an ideal plate capacitor. Thus, the structural health monitoring method developed in this work can reveal in-situ knowledge of the material damage state.

Structural Health Monitoring of Fiber Reinforced Composites Using Integrated a Linear Capacitance Based Sensor

“…The relative capacitance change curve exhibited a deviation from linear increase at a turning point for both Glass-A-1 and Glass-A-2 specimens. This turning point may indicate the onset of inter-fiber damage, where the relative capacitance change decreases or remains constant while the axial stress increases [ 27 ]. The average relative capacitance change, strain, and axial stress at the turning point were approximately 1%, 1.18%, and 208 MPa, respectively, as summarized in Table 2 .…”

“…Their research revealed that the structural capacitor deteriorated during the early stages of axial loading, coinciding with the initiation of interfacial cracking between the dielectric layers and CFRP. Recently, Buggisch et al [ 27 , 28 ] developed an analytical model that establishes a correlation between interfacial damage and a reduction in the embedded capacitance value. They embedded interleaved capacitors into GFRP (glass fiber-reinforced polymer), employing three types of electrodes, including carbon fiber yarn, narrow copper wires, and solid copper wires.…”

Electrostatic potential of a uniformly charged annulus

“…However, this system is also very important for many other applications, for instance, in the world of sensors. As a matter of fact, a charged annulus is a key component for building coplanar capacitive sensors which are used for a non-destructive evaluation of materials [24][25][26][27]. The most common design of a coplanar capacitive sensor has two coplanar electrodes, namely, plates with any given shape (square/rectangular, circular, etc).…”

Coating Glass Fibre Yarn with Conductive Materials for Real-Time Structure Sensing

“…Also, the capacitance value can be altered by changing the dielectric constant. For example, induced interfacial damages such as cracks in the epoxy matrix may allow the air to enter between layers, which in turn can alter the effective dielectric (flaws /damage detector) [8]. Also, this type of sensor can be used for detecting water intrusion in composite structures (humidity sensor) where the change of dielectric properties of the material is directly affected by the changing moisture content [9].…”