Sanghyun Yoo

Mechanical and thermal characterisation of multifunctional composites incorporating phase change materials

The paper reports an experimental investigation on the mechanical and thermal properties of multifunctional composite laminates integrated with microencapsulated phase change materials. The different microstructures were created by incorporating microencapsulated phase change materials in glass–epoxy composites at weight fraction between 0 and 20 wt.%. To characterise the mechanical properties, tension, compression and flexural tests were conducted. The scanning electron microscope studies were used to investigate the damage mechanisms associated with these loading conditions. Thermal storage capability of the multifunctional composites was characterised using heat flux meters. The apparent heat capacity of the composites was linearly proportional to the concentration of microencapsulated phase change materials. Alternative design analysis resulted in an optimised laminate configuration with high thermal storage capability coupled with excellent mechanical properties.

Durability of Embedded PZTs in Structural Health Monitoring Systems under Cyclic Loading

Structural Health Monitoring (SHM) systems are developed to decrease the maintenance cost and increase the life of engineering structures by fundamentally changing the way structural inspections are performed. However, this important objective can only be achieved through the consistent and predictable performance of a SHM system under different service conditions. The capability of a Piezoelectric lead Zirconate Titanate (PZT)-based SHM system in detecting structural flaws strongly depends on the sensor signals as well as actuator performance. But service conditions can change the behaviour of transducers, raising questions about long term SHM system capability. Although having a clear understanding of the reliable sensor life is important for surface mounted systems, however, this is particularly critical for embedded sensors. This is due to the fact that opportunity for replacement of sensors exists for surface bonded transducers while for the embedded systems, sensor replacement is not straightforward. Therefore, knowledge of the long term behaviour of embedded-SHM systems is critical for their implementation. This paper reports a study on the degradation of embedded PZT transducers under cyclic loadings. Carbon/epoxy laminates with an embedded PZT were subjected to fatigue loading and their performance was monitored using Scanning Laser Vibrometery (SLV). The functionality of PZT transducers under sensing and actuating modes were studied. High and low cycle fatigue tests were performed to establish strain-voltage relationships which can be used to identify critical cyclic loading parameters (number of cycles and R value) under sensing and actuating modes.