One of the most efficient implementations of lightweight design is the use of carbon fibre reinforced plastics due to their outstanding specific mechanical properties. With respect to multi-material-design, carbon fibre reinforced plastic parts have to be joined to other components such as load frames or functional elements. The use of embedded metal elements, so called inserts, is favoured to avoid drilling of composites. The fibre continuity is ensured and no local bearing stresses occur. In the work at hand the influence of impact damage on the quasi-static and cyclic strength was evaluated by pre-damaging the components by various impact energies. The components show only a minor reduction of the mechanical properties for impact energies up to 12 J. For impact energies between 12 J and 16 J, a loss in the mechanical properties is evident but final failure only occurred for impact energies above 16 J. Another aim of this study was to derive service-life-prognosis using multiple step tests and to validate these with experimentally determined S-N curves. Due to different damage mechanisms occurring under quasi-static and cyclic loads, a service-life-prognosis based on the multiple step tests was not feasible, however, a service-life-prognosis based on the experimental data is given.

Continuous composite extrusion represents a new possibility for the manufacturing of shape memory alloy metal matrix composites (SMA-MMC). During the process SMA wires are embedded into aluminum or magnesium profiles by means of modified porthole dies. Due to the high flexibility regarding the profile geometry, the materials as well as number, thickness and position of the SMA elements, the process can be used for the generation of a profile integrated bending function. The bending function of the actuator profile depends on the temperature and is thermally activated. The parameters influencing the behavior of the manufactured composited actuators are experimentally investigated. It is found that the radius of curvature mainly depends on the recovery stress and the eccentric position of the SMA wire as well as on the bending stiffness of the actuator profile. The bending mechanism and the experimental results are described by the use of an analytical model as well as a finite element analysis. Based on the results the analytical model is used for the targeted design of a profile with multiple embedded NiTi wires, which is able to perform a repeatable, pure elastic deflection within a defined temperature range between room temperature and 75 °C.

In shape memory alloy metal matrix composites manufactured by continuous composite extrusion the strategies of active property tuning and active strain energy tuning are used for the improvement of the mechanical properties of the components. Due to the thermal activation of the embedded NiTi wires (SM495), compressive stresses are transferred to the surrounding aluminum matrix (AA6060). At elevated temperatures tensile tests, three-point-bending tests and notch impact test show the influence of temperature, prestrain and reinforcing volume on the component performance. In tensile testing, a simultaneous increase of strength and ductility can be found, leading to an increase of the energy abortion capacity. Results of the three-point-bending test and notch impact test also show an increase of the required work depending on the thermomechanical treatment of the specimens.

Joining methods that present a detachable connection of thin walled fiber reinforced plastic (FRP) structures greatly increase the proliferation of lightweight FRP-parts. This paper describes the design of a new layer wise build insert solution named multilayer insert (MLI) in a comparative study in terms of mechanical performance. The MLI is designed to be easily integrable into existing automated fiber placement processes. The mechanical characteristics and damage behavior of the MLI is compared with a commercially available insert serving as reference. Comparable results are obtained by testing the specimen in the same test setup. Both, the results of the MLI and the reference specimen show that a geometrical optimization is able to change the failure modes of the connection thereby keeping the surrounding FRP intact while improving the mechanical performance of the entire component.

Carbon fiber reinforced plastics are promising materials for lightweight structures, for instance in automotive applications due to their outstanding specific mechanical properties. However, the load transfer in structural carbon fiber reinforced plastics parts via a detachable connection poses a challenge for the composite. Conventionally, the parts have to be drilled for this purpose whereby the fiber continuity is interrupted and hence the associated local stress accumulation decreases the load bearing capacity of the composite. This can be prevented by using embedded metal elements, so-called inserts, for joining parts in structures. The damage behavior under tensile loading of inserts turned out to be extremely complex and is based on different mechanisms. In order to understand the damage evolution under tensile loading detailed knowledge about the deformation of the insert, crack growth in the laminate and debonding between metal insert and carbon fiber reinforced plastics is necessary. This paper aims for an investigation of the insitu failure behavior during tensile loading of composite sheets equipped with two different types of inserts by means of acoustic emission and computed tomography analysis. An inductive strain gauge was additionally installed underneath the laminate when performing the tensile tests monitored by acoustic emission analysis.

Carbon-fiber-reinforced plastics (CFRPs) are gaining increasing applicability to lightweight structures (e.g., automotive applications) due to their outstanding mechanical properties. High-performance parts can be fabricated from CFRPs, but they have the disadvantages of low shear and bearing strength. To achieve detachable connections and introduce loads without decreasing the load-bearing capacity of the composite, it is important to use mechanical fasteners without drilling into the parts. To accomplish this, metal elements called inserts are embedded in the CFRP laminate. Damage behavior in a CFRP under tensile conditions has several different mechanisms, depending primarily on the deformation of the insert. This research investigates the in-situ failure behavior of the composite under tensile loads by investigating the deformation of the insert via computed tomography (CT). The results are also used for validation of the insert’s deformation using a finite-element model (FEM).

An efficient implementation of lightweight design is the use of continuous carbon fiber reinforced plastics (CFRP) due to their outstanding specific mechanical properties. Embedded metal elements, so-called inserts, can be used to join metal-based attachments to structural CFRP parts in the context of multi-material design. They differ from other mechanical fasteners and have distinctive benefits. In particular, drilling of the components to be joined can be avoided and, depending on the preforming, fiber continuity can be maintained using such elements. Thus, no local bearing stress is anticipated. Previous work published by the authors [1] dealt with a systematic research of the influence of different types of stresses on the load bearing capacity of welded inserts. This contribution aims at the investigation of the performance of shape-optimized inserts under the same types of loading to compare with the results of the welded inserts serving as a reference. For that purpose, the respective load bearing capacities were evaluated after preinduced damages from impact tests and thermal cycling. In addition, dynamic high-speed tensile tests (pull-out) were conducted under different loading velocities. It is shown that the load bearing capacities increased up to 19% for high velocities (250 mm/s) in comparison to quasi-static loading conditions (1.5 mm/min) showing an obvious strain rate dependency of the CFRP. Quasi-static residual strength measurements under tensile loading identified the influence of the respective preinduced damages of the insert. Influence of the thermal loading condition was evaluated by placing the specimens in a climate chamber and exposing it to various numbers of temperature cycles from-40 °C to +80 °C with a duration time of 1.5 hours each. Here, it turned out that already 10 temperature cycles decreased the quasi-static load bearing capacity up to 31%. According to DIN EN 6038 the specimens were loaded with different impact energies and the residual strength were measured carrying out pull-out tests. It could be shown that the damage tolerance is significantly lower for the shape-optimized insert due to failure-critical delamination. The optimized insert also endured lower impact energies and the influence on the performance was higher.

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.

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.