Abstract

Hybrid laminates consist of layers of different materials, which determine the mechanical properties of the laminate itself. Furthermore, the structure and interfacial properties between the layers play a key role regarding the performance under load and therefore need to be investigated in respect to industrial applicability. In this regard, a hybrid laminate comprised of AA6082 aluminum alloy sheets and glass and carbon fiber-reinforced thermoplastic (polyamide 6) is investigated in this study with a focus on the influence of aluminum surface treatment application on tensile and fatigue behavior. Four different aluminum surface treatments are discussed (adhesion promoter, mechanical blasting, phosphating, and anodizing), which were characterized by Laser Scanning Microscopy. After the thermal consolidation of the hybrid laminate under defined pressure, double notch shear tests and tensile tests were performed and correlated to determine the resulting interfacial strength between the aluminum sheet surface and the fiber-reinforced plastic, and its impact on tensile performance. To investigate the performance of the laminate under fatigue load in LCF and HCF regimes, a short-time procedure was applied consisting of resource-efficient instrumented multiple and constant amplitude tests. Digital image correlation, thermography, and hysteresis measurement methods were utilized to gain information about the aluminum surface treatment influence on fatigue damage initiation and development. The results show that fatigue-induced damage initiation, development, and mechanisms differ significantly depending on the applied aluminum surface treatment. The used measurement technologies proved to be suitable for this application and enabled correlations in between, showing that the hybrid laminates damage state, in particular regarding the interfacial bonding of the layers, can be monitored not just through visual recordings of local strain and temperature development, but also through stress-displacement hysteresis analysis.

Highlights

  • Hybrid laminates of light metals and fiber-reinforced plastics (FRP), known as Fiber MetalLaminates (FML), combine the advantageous properties of both material groups in one material compound

  • These material compounds are of great importance, especially as structural materials in aircraft construction compared to conventional aluminum alloys, due to the lower crack growth based on the fiber bridging effect [1,2,3]

  • Materials 2020, 13, 3080 especially in the field of mechanical and fatigue properties is based on GLARE, which is a multi-layer combination of aluminum alloy AA2024 and glass fiber-reinforced epoxy resin layers [3,4,5,6,7,8,9]

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Summary

Introduction

Hybrid laminates of light metals and fiber-reinforced plastics (FRP), known as Fiber MetalLaminates (FML), combine the advantageous properties of both material groups in one material compound. Besides a better damage tolerance compared to FRP, the FML have a lower density and higher strength than monolithic metal alloys. These material compounds are of great importance, especially as structural materials in aircraft construction compared to conventional aluminum alloys, due to the lower crack growth based on the fiber bridging effect [1,2,3]. Materials 2020, 13, 3080 especially in the field of mechanical and fatigue properties is based on GLARE, which is a multi-layer combination of aluminum alloy AA2024 and glass fiber-reinforced epoxy resin layers [3,4,5,6,7,8,9]. Hybrid laminates based on fiber-reinforced thermoplastics in combination with aluminum alloys of the 5000 and 6000 series are an interesting alternative.

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