Kay André Weidenmann

Mechanical Properties of Compound-Extruded Aluminium-Matrix Profiles under Quasi-Static Loading Conditions

Compound-extruded unidirectionally reinforced lightweight profiles are a novel class of materials for the realisation of load-bearing structures. They may be fabricated in a flexible and rapid near-net-shape process. The authors present investigations of the reinforcing effect of wires in compound-extruded aluminum profiles under quasi-static tension and compression. In particular, the compounds were characterized by metallographic examinations focusing on the fracture morphology. Furthermore, specimens subject to compression tests were examined using micro computer tomography (µ-CT) and light microscopy (LM). It is shown, that the mechanical properties of wire-reinforced profiles are improved under both positive and negative quasi-static loads in comparison to non-reinforced profiles.

Tensile behaviour of spring steel wire reinforced EN AW-6082

The reinforcement of composite aluminium extrusions offers a high potential regarding weight reduction and improvement of mechanical properties, which is essential for components in lightweight constructions. The current work gives an overview of the quasi-static properties of spring steel wire reinforced EN AW-6082 with varying reinforcing ratio. The deformation and damage behaviour is investigated in detail for a reinforcing ratio of 11.1 vol.%. It is shown that the relatively ductile behaviour of the spring steel wire leads to multiple necking resulting in higher strains than expected. Current models are expanded and modified for a proper adaptation to the material system.

Characterization of Metal Inserts Embedded in Carbon Fiber Reinforced Plastics

The use of fiber-reinforced-plastics (FRP) contributes to an efficient implementation of lightweight design due to their outstanding specific mechanical properties. The RTM process offers great design freedom and allows the integration of functional elements during manufacturing. Embedded metal elements, so-called inserts, can be used to deal with the load transfer to structural parts. These elements have distinctive characteristics in comparison to other joining technologies. For example, detachable connections can be established with the help of inserts. Due to the fiber continuity not being interrupted and, subsequently, the FRP parts not having to be drilled, there is no local bearing stress. This paper aims at the characterization of metal inserts in FRP parts. The parts are manufactured using the RTM process with a specially adapted RTM mold with exchangeable cartridges for different insert geometries. The inserts are made of metal sheets with welded bushings and are embedded during preforming. The cured FRP specimens are tested under different load conditions to evaluate their suitability for various fields of application. Furthermore, the diameter and thickness of the metal sheet of the insert as well as the thickness of the FRP are varied to identify their influence on the failure behavior and load capacity under tensile loads.

Characterization of the interfacial shear strength of glass-fiber reinforced polymers made from novel RTM processes

In this study, three different glass fiber reinforced polymers have been investigated with respect to the interfacial shear strength. Conventional resin transfer molding (RTM) and the compression RTM (CRTM) process for the production of reinforced samples with an epoxy matrix were chosen. The third process was a thermoplastic RTM (TRTM) process for producing composites with a thermoplastic polyamide 6 matrix. Fiber type and coupling agent were not varied. The interfacial shear strengths reached by the different processing routes were determined by push-out tests. It is shown that the RTM interface shear strength is very high and comparable to that generated by the CRTM process, despite increased fiber fracture for the RTM samples. The TRTM process yielded significantly lower interfacial shear strength values. Plastographic analysis of the material systems showed the formation of an interfacial layer between the fibers and the thermoset matrix. For the thermoplastic matrix a significant lower formation of crystalline spherulites at the interface and no interfacial layer could be observed.

Influence of heat treatment on the properties of AlSi10Mg-based metal matrix composites reinforced with metallic glass flakes processed by gas pressure infiltration:

The reinforcement of a soft matrix material with hard particles is an established strategy to develop materials with tailored properties. In this regard, using metallic glasses with high crystallization temperatures, e.g. in the system NiNbX (X = Sn, Ta), for composites produced by liquid metal infiltration is a novel approach. The current work deals with the characterization of such metallic glass particle-reinforced AlSi10Mg-based metal matrix composites manufactured by gas pressure infiltration. Processing–structure–property relations were investigated with a special focus on the influence of an additional heat treatment on the metal matrix composite’s properties. Metallographic methods were used to investigate infiltration quality, particle distribution within the composite and the composite’s microstructure. Moreover, X-ray diffraction measurements, elastic analysis using ultrasonic spectroscopy and compression tests were performed to analyze its properties. The X-ray diffraction results indicate that there is no crystallization of the glass during processing. Metallographic investigations show that the flakes are arranged in a layered structure within the composite. The embedding of metallic glass flakes leads to an increase in Young’s modulus and compressive strength in comparison to the unreinforced material. The composite’s strength can be further increased by a heat treatment.

Characterization of a hybrid Al2O3–aluminum matrix composite manufactured via composite extrusion

The development of new metal matrix composites for lightweight applications is aiming for an increase in specific strength and stiffness compared to conventional light metal alloys. The composite extrusion process is a promising manufacturing method for continuously reinforced light metal profiles. Especially the reinforcement with ceramic fibers leads to an increase in the specific strength and stiffness. For these investigations a hybrid composite is produced by using an Al2O3-fiber/AlMg0.6 composite wire which is embedded in an EN AW-6082 aluminum matrix. It is shown that the mechanical properties of the composite exceed those of the unreinforced matrix material. An explicit investigation of the deformation and damage behavior of this composite is given by optical strain analysis and in situ tensile tests in an X-ray micro computed tomograph (µ-CT). It was observed that during tensile loading multiple fracture of the composite wire occurs while exceeding the strain limit of the non-embedded composite wire. It could be shown that fracture of the composite wire is accompanied by strain localization and therefore strain hardening occurs in vicinity of the internal fracture, which leads to multiple necking of the specimen. The µ-CT analysis reveals the intrinsic damage mechanisms and shows the beginning of ceramic fiber fracture which showed evidence for a local load distribution between the fibers resulting in a planar fracture of the composite wire. The multiple fracture of the wire allows for an interface shear strength analysis and indicates a good bonding of the composite wire.

Mechanical properties of rope-reinforced aluminium extrusions under quasistatic loading conditions

Abstract Compound-extruded unidirectionally reinforced lightweight profiles are a novel class of materials for the construction of load-bearing structures. In this paper, investigations of the reinforcing effect of ropes in compound-extruded aluminium profiles tested under quasistatic loading conditions are presented. In particular, the investigations lead to a characterisation of the interface between matrix and reinforcing element, as the compounds internal load transfer is a crucial factor in the overall mechanical properties. It could be shown that – in addition to a form fit – a diffusional bond evolves. Both Youngs modulus and tensile strength could be increased by using a rope reinforcement. Furthermore, the results attained are compared to a theoretical model which was adapted to the deformation behaviour of compounds containing a single reinforcement.

Optimization of corrosive properties of carbon fiber reinforced aluminum laminates due to integration of an elastomer interlayer

Fiber-Metal-Laminates (FML) show superior dynamic mechanical properties combined with low densities. The mechanical performance of for example commercially available fiber-metal-laminate, glass laminate aluminum reinforced epoxy, can be improved by the substitution of glass fibers with carbon fibers. However, carbon fiber reinforced aluminum laminate introduces a mismatch of coefficients of thermal expansion and the possibility of galvanic corrosion. The fiber-metal-laminate is altered by the integration of an elastomer interlayer which is desired to solve both problems. The high electrical resistance is supposed to inhibit the corrosion. This study focuses on the effect of galvanic corrosion caused by neutral salt spray tests on fiber-metal-laminates, the influence of an elastomer interlayer and the quantification of the residual mechanical properties. The galvanic corrosion affects the interfaces of the laminates, therefore in this study edge shear tests and flexural tests were carried out to quantify the residual properties and thereby the corrosive damage. The elastomer interlayer was found to inhibit galvanic corrosion in the salt spray chamber, whereas the fiber-metal-laminate without interlayer showed corrosive damage. Furthermore, the mechanical properties of the fiber-metal-laminate with elastomer interlayer remained constant after the corrosion tests, whilst the fiber-metal-laminate’s properties decreased with corrosive loads.

Specific bending stiffness of in-mould-assembled hybrid sandwich structures with carbon fibre reinforced polymer face sheets and aluminium foam cores manufactured by a polyurethane-spraying process [in press]

In this paper, the bending stiffness-to-weight-ratio of novel hybrid sandwich structures is investigated. The build-up of the sandwich panels consisted of face sheets made from carbon fibre reinforced polymer, aluminium foam cores and an interface of foamed polyurethane. The sandwich panels were produced in a single step, infiltrating the face sheet fibres and connecting the face sheets to the core simultaneously. By means of mechanical characterization, specimens with several variations of face sheet architecture and thickness, core structure and interface properties were examined. Quasi-static four-point bending and flatwise compression tests of the sandwich composites were conducted, as well as tensile tests of the face sheets. The results of the tensile and compressive tests were integrated in analytical models, describing the sandwich stiffness depending on the load case and the face sheet volume fraction. The effective Young’s modulus of the composite, measured in the four-point bending test, correlates well to the modelled effective bending modulus calculated from the single components face sheet and core. The model underestimates the effective density of the bending specimens. It could be shown that this underestimation results from the polyurethane foam connecting the face sheets to the core, as the mass of this polyurethane is not included in the model.

Shear edge tests: a benchmark in investigating the influence of different surface pretreatment methods on the shear stress of intrinsically manufactured metal-CFRP hybrids

At the present time, environmental protection and efficient energy and resource usage are key topics in the industrial sector. In contrast, the desire for comfort, mobility and protection increases progressively and leads to an immense weight gain. Particularly, in the automotive and aerospace industry, strong efforts are made to ensure an efficient manufacturing of lightweight structures. Thereby, an upcoming trend is represented by the application of hybrid structure manufactured by innovative procedures. One of these is the resin transfer moulding procedure, which ensures a highly automated one-step manufacturing of hybrid structures consisting of metal and carbon fibre-reinforced plastics (CFRP). In many cases, the generation of a strong and durable connection between the dissimilar materials is one of the major challenges. In this study, the influence of various surface pretreatment methods on the shear strength of the hybrid structures out of aluminium or steel and CFRP is investigated. In order to eliminate the influence of bending moments and specific material properties, shear edge tests, which enable a pure shear load, are carried out. Furthermore, the failure behaviour is analysed. It is shown that the shear edge test represents an excellent benchmark test to obtain precise interface properties such as shear-stress and fracture work. These properties can be significantly enhanced using surface pretreatment methods.