Influence of Aluminum Surface Treatment on Tensile and Fatigue Behavior of Thermoplastic-Based Hybrid Laminates

Abstract

<jats:p>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.</jats:p>

Testing Procedure for Fatigue Characterization of Steel-CFRP Hybrid Laminate Considering Material Dependent Self-Heating

“…This combination of CFRP and steel form a generic model material, without a specific industrial application but for the special purpose of developing a testing procedure. To improve the adhesion between the materials through surface treatment of the metal layer [ 20 , 21 , 22 , 23 ], the steel sheets were grid blasted with alumina. In addition, polymer foil (PA6, thickness 0.05 mm) was placed between composite and metal layers to improve adhesion, as the excess polymer fills the roughness of the blasted metal surface ( Figure 1 ).…”

Pin-Shaped Surface Structures Generated by Laser Single Pulse Drilling for High-Strength Interfaces in Thermally Joined Polymer–Metal Hybrids

“…For surface pretreatment, mechanical blasting with, e.g., alumina is an industrially established, low-cost process for creating stochastically arranged, rugged structures that can achieve acceptable adhesion [ 4 , 5 , 6 , 8 , 12 , 20 , 34 , 47 , 48 , 49 ]. However, laser structuring is by far the most investigated pretreatment method.…”

Novel AA7075/AA2124-SiC-17p laminated structures for aerospace applications: A Comparative study into the mechanical performance of PA6 and PA66 composite interlayers

“…The surface pretreatments of metallic materials such as mechanical modification or chemical etching can enhance the adhesion and wettability between polymer and metal, which may contribute greatly to the mechanical performance of hybrid structures. 46,47 To date, few investigations have been carried out to evaluate the metal-polymer-metal layered hybrid structures. Richter et al 48 investigated the interface properties of steel-PP/PE polymer-steel sandwich sheet with the Double Cantilever Beam (DCB) test.…”

“…The surface pre-treatments of metallic materials such as mechanical modification or chemical etching can enhance the adhesion and wettability between polymer and metal, which may contribute greatly to the mechanical performance of hybrid structures. 46,47…”