This particular research constitutes a research and development project; a novel technique for the embedment of highly thin (nearly zero-thickness) defects in aerospace grade adhesively bonded composite joints is the dominant subject. These defects consist a representative of poor polymer processing and impact induced defects, while this project studies the mechanical response of the joints in the presence of such defects. This was assessed using composite-to-composite single-lap joint (SLJ) specimens having different width and defect type. With respect to this project, two categories of defects with two different widths were recognised for laboratory testing; therefore, four configurations were considered. The joints were manufactured via manual lay-up of carbon fibre-reinforced composite prepreg and autoclave curing, followed by non-destructive inspection (ultrasonic C-scan, pulsed-echo thermography and infrared thermography) as an attempt for detecting embedded zero-thickness defects. The joints were then subjected to mechanical tension loading to determine the ultimate failure load and displacement. Finally, the fracture area of the failed joints in the bond area was observed with optical microscopy to visualise and determine the failure mechanisms, i.e. cohesive and adhesion failure.

Chapter Contents:

• 14.1 Introduction
• 14.1.1 Aim
• 14.1.2 Objectives
• 14.2 Materials and manufacturing
• 14.2.1 Materials
• 14.2.2 Manufacturing
• 14.3 Testing
• 14.3.1 Lap shear test
• 14.3.2 NDI
• 14.4 Results and discussion
• 14.4.1 Lap shear test
• 14.4.2 NDI
• 14.4.3 Optical microscopy
• 14.5 Conclusions
• References

Inspec keywords: composite materials; failure (mechanical); adhesive bonding; impact (mechanical); optical microscopy; inspection; aerospace materials; ultrasonic materials testing; fracture; adhesion; infrared imaging; carbon fibre reinforced plastics; curing; polymers

Other keywords: mechanical tension loading; optical microscopy; ultrasonic C-scan thermography; polymer processing; failure mechanisms; nondestructive inspection; fracture area; pulsed-echo thermography; carbon fibre-reinforced composite prepreg; laboratory testing; adhesively bonded composite joints; infrared thermography; process-induced defects; aerospace composites; adhesion; zero-thickness defects; single-lap joint; autoclave curing; impact induced defects

Subjects: Fracture mechanics and hardness (mechanical engineering); Adhesion (mechanical engineering); Engineering materials; Testing; Inspection and quality control; Ballistics and mechanical impact (mechanical engineering); Industrial processes; Aerospace industry