Damage progression and failure characteristics of open‐hole flax fibre aluminium laminate (flax‐FML) specimens subjected to quasi‐static tensile or tension‐tension fatigue loading were experimentally investigated. Notched and unnotched flax‐FML composites exhibited brittle fracture with little or no fibre pull‐out and minimal delamination at the aluminium/adhesive interface. The flax‐FMLs were tested to failure under tension‐tension fatigue loading conditions (Rratio of 0.1; frequency of 10 Hz; applied fatigue stresses ranging between 30% and 80% of the respective ultimate tensile strength values). The fatigue cycles to failure decreased with the increase in the applied fatigue stress and hole diameter. A phenomenological modelling technique was developed to evaluate the fatigue life of an open‐hole flax‐FML composite. Fatigue tests on specimens subjected to a maximum load equivalent to 35% of the respective tensile failure strength were interrupted at around 85% of the corresponding fatigue life. The accumulated fatigue damage in these specimens was characterised using X‐ray computed tomography. For benchmarking purposes, the fatigue performance and related damage progression in the flax‐FML composite were compared with those of the glass‐FMLs.

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.

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.

Automated fibre placement (AFP) has emerged as a prominent manufacturing technique in the aerospace industry for producing high-performance composite structures. However, defects such as gaps and overlaps inevitably occur during the AFP process, and can significantly influence the end-product quality of composite structures. Compression strength can play an important role in composite structures, especially in the residual load-bearing capability in presence of damages, and its characterisation is necessary for the correct sizing of structures. To evaluate their impact on mechanical properties, dynamic compression testing of carbon fibre-reinforced low-melt polyaryletherketone (CF/LM-PAEK) is conducted using a high-speed test machine. An end-loading compression fixture with honeycomb is used to perform dynamic compression tests at strain rates up to 200 s ⁻¹ . Ultrasonic C-scan images of as-manufactured defects in test specimens are examined to correlate the contents of gap defects and compressive strength. The results show a clear strain-rate effect on compressive strength within the range of tested strain rates. Also, a transition of failure modes from kink band to wedge splitting is observed at high strain rates. No clear correlation between the gap contents and compressive strength is identified. Those results indicate that the staggered gaps in tested specimens have a minimal impact on compression properties. The findings from this experimental study highlight the effect of defects induced by AFP manufacturing processes on compressive properties at intermediate strain rates. This research contributes to a deeper understanding of the complex relationship between AFP-induced defects and strain-rate effects, providing valuable insights into designing AFP components.