Fatigue behaviour of material-adapted fibre-reinforced polymer/metal joints

By regarding the needs and requirements in modern multi-material joining, the Flow Drill Joining Concept (FDJ) was developed at the Chemnitz University of Technology. The technology allows an efficient and material-adapted joining of thin metal sheets with continuous fibre-reinforced thermoplastics, as required in modern lightweight engineering. For a better understanding of their fatigue behaviour, single-lap FDJ joints were examined in quasi-static and dynamic tests regarding shear loads, cross tension and superimposed shear/cross tension loads. By way of example, joints between micro-alloyed steel with high yield strength for cold forming and a continuous glass/carbon fibre-reinforced polyamide 6 were investigated. The fatigue curves show inclinations between k = 8.01 (shear loads) and k = 5.17 (cross tension loads), depending on the applied load angle. The results of the fatigue testings represent a basis for the enhancement of a failure criterion for FRP/metal joints in highly stressed multi-material designs.

Analytical modelling of continuous fibre-reinforced thermoplastics’ thermomechanical properties and implementation into a failure model

Mechanical properties of fibre-reinforced thermoplastics show a remarkable temperature dependence within application temperatures of automotive and aerospace lightweight structures. To take this dependence into account when designing components, the strengths (, , , , ) and stiffnesses (, , , , ) of continuous carbon and glass fibre-reinforced polyamide 6 and glass fibre-reinforced polypropylene are modelled analytically based on experiments. Data from temperature-controlled tests on flat samples in the range from -20 °C to +80 °C are therefore approximated using an extended hyperbolic approach. The models obtained are then evaluated based on their deviation from the experimental values. The main criterion of this evaluation is the reliable prediction of the temperature-dependent material properties while minimising the effort for generating test data and determining model parameters. Furthermore, the failure behaviour of the investigated materials under multiaxial mechanical and thermal stress is examined by implementing the determined strength curves into Cuntze’s physically based failure criterion.

Application of load-adapted hybrid textiles for a thermoplastic seat pass-through

The potential of a continuous non-crimp fabric (NCF) process with implemented offset technologies is demonstrated by a case study of a seat pass-through. Topology optimization with the relevant load cases and the construction of a load-adapted composite design with a weight saving of up to 18 percent is presented. Inverse draping identifies a two-dimensional development of the construction and prepares it for production based on the restrictions of textile technology. The downstream process capability of textiles produced in this way was investigated by impregnating heavy tows with polypropylene on laboratory scale and subsequent material characterization of the resulting laminates. The impregnation and consolidation of the seat pass-through is performed with load path adapted semi-finished products using novel variothermal, fluid-based pressing. This allows better control over the dynamic impregnation and unwanted fiber washing due to the large gradient of the areal weight. The final processing in injection molding tool of the reference component shows the applicability of the technology also in existing process chains and illustrates the potential of the consistent consideration of a load-adapted composite design in the development process.

Surface irregularities in titanium marine parts formed by the particulate injection moulding process

In this study, a structural hold down component was designed and produced using the particulate injection moulding (PIM) process. The material of choice was titanium due not only to the material properties but also due to the desire to create custom-made components for a state-of-the-art marine vessel, Earthrace 2.On removal from the mould, the green parts were seen to have an irregular surface on the top face. Known as surface bloom, it can be seen during moulding of single-phase commodity polymers as a result of changes in the polymer density, due to shear stresses and irregularities of turbulent flow.Literature suggests the surface bloom is a result of a separation between the two phases, but the preliminary findings show little evidence of this within the sectioned profile. The sintered parts were sectioned, and inspection of the surfaces was done using metallographic techniques. The use of CAD models enabled the defect to be modelled and the models provided a more likely scenario. It was further confirmed that there were no through part defects present and although the surface irregularities were caused by separation of the two-phases, the effect was restricted to the outer surface of the parts.

Strain measurements with fibre Bragg grating sensors under inhomogeneous deformations

Bragg grating sensors are fibre optic sensors for strain and temperature investigations with many advantages: the sensors can be embedded in plastic materials or composites and several gratings can be inscribed in one sensor. However, inhomogeneous deformation or transversal loading cause widening and splitting of the reflected wavelength peak of a fibre Bragg grating (FBG) sensor. These effects are shown in a residual stress analysis, in which the hole drilling method is adapted for FBG sensors. Additionally, a four-point bending test on three different notched aluminium beams is used to investigate the widening and splitting of the reflected peaks and their effects on the strain analysis. At each sample, a reference strain gauge sensor and two FBG sensors are applied. The two FBG sensors are loaded with different strain gradients. The unnotched beam and the beam with small strain gradient show the accuracy and reproducibility of the experiment. The beam with medium strain gradient shows no peak splitting, but the widening does influence the strain analysis. The results of the beam with high strain gradient demonstrate the peak splitting and the failure of the strain analysis methods. Initial approaches on how to deal with this widening and splitting are discussed.

Multifunctional FRP-Aluminum Foam Production Setup for Battery Housings of Electric Vehicles

The battery systems of electrified vehicles are characterized by increasing weight due to larger battery modules. A lightweight battery carrier structure can reduce the system weight by replacing heavy metallic housing components with materials such as fiber-reinforced plastics (FRP) and aluminum. The battery housing must meet several requirements, e.g. stiffness, crash and intrusion protection and thermal management. Today’s battery housings are manufactured using die-cast or extrusion parts and are actively cooled. A novel approach is a lightweight hybrid battery housing consisting of a thermoformed FRP as a stiff outer shell and an integrated closed-cell aluminum foam infiltrated with phase change material (PCM) for passive thermal management. This multi-material structure enables the substitution of functionally separated systems in one intelligent solution. In the Open Hybrid LabFactory an entire process chain was established, including the aluminum foaming process, the thermoforming of FRP with heating and consolidating as well as the integrated forming and joining process of FRP with aluminum foam. With the goal of application-oriented research, a battery housing of an existing electric car was used to define requirements such as design space and mechanical specifications. Based on parameter studies an optimized process design was achieved, which is described in this paper.

Technology fusion of metal injection moulding and selective laser melting for the manufacture of complex and multifunctional (hydraulic) components

Selective laser melting (SLM) and metallic injection moulding (MIM) are established processes for the production of high-performance metallic components for small and large series. In the aerospace industry, where very high demands are placed on materials and components, both processes are still considered to be relatively new. In both processes, the conventional titanium alloy Ti-6Al-4V can be used in the form of powder. Currently, both technologies are only considered separately. By fusing components of the same type, multifunctional components with a high lightweight construction potential can be produced. In order to generate direct material fusion, the MIM component must be mechanically processed accordingly. In addition, suitable SLM process parameters must be developed in order to ensure both generative construction and high joint strength. To this end, a characterisation of the joining zone and the static joint strength was carried out. Furthermore, pressure test samples were designed and examined both statically and for fatigue strength. Thus, a high static joint strength could be proven. The compression test samples also withstood a fatigue strength of over 1 million cycles.

Extrusion of screws with sensor functionality

The use of components with embedded sensors is one of the most promising trends in civil engineering, plant construction and mechanical engineering. These components make it possible to both monitor the design state in real time and to recognize failures in parts and components early on. However, due to high product costs, their wider distribution is limited. Optimization of the component manufacturing technology can contribute to reducing the production costs.Fasteners, such as screws and rivets, consisting of a polypropylene composite core filled with piezoceramic powder represent a potential approach. In the event of a sudden impact, this compound generates an electric pulse, and through machine learning the cause of the failure can be filtered out from the screw’s normal state.Simultaneous forming of aluminum and plastics opens up new opportunities to produce the abovementioned screws at a reasonable price. The authors’ aim was to demonstrate feasibility through initial experiments and the generation of a simulation model.

Bicycle frame from hemp fibre filament wound composites

This work presents an initial study for hemp fibre produced in Thailand. The study focuses on the application of the filament winding technique in the production of hemp-epoxy composite tubes for a bicycle frame. The motivation is to produce hemp fibre composites from locally available resources in Thailand. For the initial trail, existing bicycle steel tubes were replaced by ±45° filament wound hemp-epoxy composites with thin aluminium inner layers. The mechanical properties of the hemp-epoxy composites were studied according to the ASTM standard. Two static load cases were chosen and considered for a 100 kg cyclist sitting on the saddle and pedalling while standing. The internal forces and moments were calculated for the frame and frame tubes. The stress and buckling analyses were performed using the finite element method for frame tubes considering the above loading cases. The finite element analysis shows that hemp-epoxy composite tubes with ±45° fibre orientation can be used as bicycle frame tubes and meet the design specifications under the considered static load conditions. The filament winding process was accomplished successfully at KMUTNB using an automated desktop filament winding machine.

Life cycle engineering and management methods for designing hybrid structures – cases, potentials, and challenges

Designing sustainable systems that take into account production factors, processes, and/or products is becoming more and more important. It is therefore the focus of research projects such as the Federal Cluster of Excellence EXC 1075 “MERGE Technologies for Multifunctional Lightweight Structures”, which strives for resource-efficient lightweight construction and especially the design of hybrid structures. To support this challenging task, the Life Cycle Engineering (LCE) approach is recommended. However, a sustainable design requires an economic or rather management orientation of the engineering activities, which is underrepresented in the LCE concept. Therefore, it is proposed to extend the LCE to a Life Cycle Engineering and Management (LCEM) concept. Since both concepts are relatively new, only a few cases of application are available. Therefore, this paper describes and analyzes cases – especially on the basis of MERGE research objects –, to which LCE and LCEM are applied, identifies potentials and challenges, and derives consequences for further research activities. This highlights the relevance of LCE and LCEM for research projects, especially regarding the transformation of an invention into a successful innovation.