Piezoresistive Sensing Approaches for Structural Health Monitoring of Polymer Composites—A Review

Abstract

Structural health monitoring (SHM) is an emerging paradigm of real-time in situ structural evaluation for the detection of damage and structural degradation. This is achieved while the structure is kept in-service as against traditional non-destructive evaluation (NDE) techniques which require scheduled interventions while the structure is kept offline. SHM offers great advantages over traditional regimens of condition monitoring (CM) by improving structural reliability and safety through timely detection of structural defects also known as “diagnosis”. Polymeric composite materials offer the unique opportunity of integrating different phases for designing self-sensing smart systems capable of self-diagnosis. Polymers are unique in the sense that they can be designed in various configurations as they generally have facile manufacturing procedures. Among other properties, piezoresistance is the one that can be detected in composites in real-time as a function of strain. Conductive polymers including intrinsic and extrinsic conductive polymers can be used to induce piezoresistivity in composites. Careful design procedures can be adopted to maximize the sensitivity of these piezoresistive composites in order to fully exploit the potential of this property for SHM. Various manufacturing/integration strategies can be employed to effectively use piezoresistance in composites for structural health monitoring. These include self-sensing in carbon fiber-reinforced composites, use of surface deposited/mounted sensing films and patterns, integration of filaments and yarns during reinforcement manufacturing or lay-up and impregnation of reinforcements with piezoresistive matrices. A comprehensive review of these techniques is presented with the view of their utility in the SHM of composites. A selection criterion for these techniques is also presented based on sensitivity, manufacturing method and detection capability.

Comparison between Piezoelectric and Piezoresistive Wearable Gait Monitoring Techniques

“…When the concentration of added conductive fillers meets the percolation threshold, the conductive filler forms a percolation network that permits the electrons to move from one filler particle to another one [ 26 ]. This is also known as electron tunneling, which indicates the material has become conductive, which enables the conductivity of extrinsic polymers to be adjusted to achieve piezoresistivity [ 27 ].…”

“…To achieve this purpose, suitable methods include doping particles into intrinsic polymers or heating. Therefore, the released electrons increase the conductivity of the material to achieve piezoresistivity [ 26 , 27 , 28 ]. Figure 2 illustrates the mechanisms of conductive intrinsic and extrinsic polymers.…”

“…For example, carbon nanotubes and graphene-based sensors have high mechanical flexibility and stretchability; they can maintain high sensitivity under bending and pressing. Therefore, they can be used for PSD [ 4 , 5 , 7 , 12 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ].…”

“…However, the modulus of sensing material increases with working time, which can decrease sensitivity and cause potential hysteresis [ 14 , 19 ]. Additionally, hysteresis and temperature [ 26 , 27 ] also decrease sensor accuracy.…”

Smart Graphene Nanoplatelet Strain Sensor for Natural Frequency Sensing of Stainless Steel (SS304) and Human Health Monitoring

“…In addition, GNPs enhance the microstructure and viscoelastic characteristics of PMMA. Smart sensors, especially made from graphene materials as substrates, have been studied [ 13 , 14 , 15 ]. Substrates such as PMMA have been studied as reinforcement carbonaceous filler for obtaining well-dispersed alignment-based nanocomposites with GNP.…”