Key Engineering Materials Vol. 742

Abstract: Aluminium-polymer laminate foils consisting of the layers PA, Al and PVC are used to manufacture high barrier pharmaceutical packages. These so called cold-formed blister packs are formed by stretch forming at room temperature. As due to the complex material structure the forming process is not yet well understood, the developers of cold-formed blister packaging machines design the punches for forming the cavities bigger than needed for the tablets being packed. Therefore, the aim of this work is to gain insight into the mechanical behavior of the composite during stretch forming. For this, internal and residual stresses in the layers are analyzed with the finite element method. With the help of a micromechanical and a stretch forming model simulations are performed. Furthermore, an analytical solution to calculate the internal and residual stresses during stretch forming the foil is presented. The calculation procedure can be used to determine stresses from surface strains which could be measured in forming experiments.

Abstract: Within the European research project ECOMISE advanced process simulation methods have been developed. Existing Software tools like RTMWorx and NX CAE have been extended in their capabilities and interface have been developed between them to have a direct data communication. In the present case a manufacturing process of a tidal blade was used to test and validate the development. In RTMWorx a new 3D solution was developed and an a import interface to read direct a structural model from NX with all related information’s like geometry, mesh and layup. The interface reads the ply information’s and calculates resulting permabilities for the layup. In NX CAE also interfaces and mapping algorithm have been developed to read information’s like filling factors from RTMWorx. In combination with the new functionalities to simulate curing, process induced deformation and residual stresses the virtual process chain enabling a complete analysis of the whole manufacturing process starting from a initial design with capabilities on draping including direct ply contour creation, infusion, curing and analysis of process induced deformation.

Abstract: The present contribution aims to investigate the ability of drawing predictive conclusions from homogenization in case of damage. Therefor, two topics will be addressed. On the one hand, material properties for the constituents on the microscale have to be derived, to render a predictive homogenization possible. The investigation at hand is concerned with glass fiber reinforced epoxy resin. In this example the properties of the fiber and the matrix have to be studied individually by experiments. Furthermore, the interface between both materials needs to be examined. To this end experiments on several models of single fiber composites have been developed in the literature. For the present material combination single fiber fragmentation tests and pullout tests have been conducted and evaluated. On the other hand, boundary conditions are necessary, that allow for the strain localization in a volume element without leading to spurious localization zones.

Abstract: Fiber reinforced polymers (FRP) are used in a widespread range, for example in aerospace, mobility or wind energy applications due to their excellent quality profile. Moreover, rotating machine elements, which are applied in dynamic processes, require a primarily high stiffness combined with an elastic behavior. Novel FRP components or modern hybrid structures lead to a lower energy consumption of the entire mechanical system. In this respect, a shaft coupling between two shafts depicts an exemplary machine element for a possible application of FRP. This paper deals with the numerical analysis on the structural behavior of a non-engaging bellows coupling made of prepreg-based carbon fiber reinforced polymers (CFRP) for propulsion technology. The presented concept is based on the methodological construction approach for the fulfillment of the compensation and connection functionality. A very high torsional stiffness as well as a certain bending flexibility of the whole coupling geometry is required due to the connection of two torsion-loaded structures. Specific geometrical design variables could be identified with the finite elements method (FEM) and the design of experiments (DoE), which have a significant influence on the structure mechanical behavior of the CFRP bellows coupling. Based on a variable identification scheme according to Shainin, the influence of various geometrical design factors on the structural performance of the CFRP bellows coupling was evaluated.

Abstract: This work presents the influence of deviations of fiber orientations of warp and weft yarns to the shear stress vs. shear angle behavior and the formation of wrinkles of fabric reinforced thermoplastics. FE results of bias-extension tests and the forming of a double dome part will be investigated with angular misalignment of the yarns and/or deviations of the blank to its loading direction. The prepregs or organic sheets may have imperfections like fiber misalignment or the prepregs of multilayered sheets are twisted against each other. Furthermore, there may be deviations to the idealized orientation caused by the operator or cutting machine for example.

Abstract: Objective of the present study is the definition of a material model accounting for fatigue damage and degradation. The model is formulated as a brittle damage model in the otherwise linear elastic framework. A stress driven damage evolution equation is derived from microplasticity considerations. The model is implemented as a user-defined material model into a commercial finite element program. In a comparison with experimental data in the low cycle fatigue regime, a good agreement with the numerical prediction is obtained.

Abstract: Commercial vehicles are mostly equipped with pneumatic spring elements which lead to a perfect height levelling and spring rate adjustment under different loading conditions. However, pneumatic springs are not common in light commercial vehicles where passive spring elements, e.g. single- and multi-leaf springs, are still be used. Since those vehicles are covering a wide range of different loads the spring elements frequently exhibit a progressive spring characteristic, i.e. the spring rate is adjusted under deflection as soon as the load is increased. The need for light weight design also relates to light commercial vehicle so that glass fibre reinforced plastic (GFRP) has become a suitable substitute for high strength steel. Furthermore GFRP allows for innovative as well as functionally and technologically improved constructional solutions of progressive spring elements, e.g. the single-leaf spring approach by Schürmann et al [1].However, the above mentioned solution is sometimes rather solitaire and no systematic approach for its genesis exits. Hence, this contribution shows an approach for a more systematic development of progressive light weight spring element concepts in vehicle construction. Different approaches of implementing a progressive spring rate characteristic are presented in the introduction. A simple analytical model of a bending beam considering a variety of boundary conditions has been set up to discuss the effect of bearing stiffness on the spring rate.The model serves as a basis for a kind of toolbox for a more systematic approach for the development of the desired progressive spring elements. It allows to identify and to select a balanced concept for a progressive light weight spring element which also considers the application of the appropriate spring material at any specific part of the construction.

Abstract: Combined with shared service points in prime locations the use of Light Electric Vehicles (LEV) can help optimize the cost expensive „last mile“ of parcel service. [1] At the same time, a shared service point enables the switch from diesel driven engines to muscle-powered electric driving in cities. It is known, that in city operating courier services up to 80 % of actual used diesel fuel can be substituted by muscle supported electric driving. [2] To cover the needs of global operating parcel services a muscle-power supported LEV must meet the requirements of ergonomics (regarding usability in the modes drive and delivery) and parcel security. To gain economic benefits the construction of LEV for parcel delivery should be flexible enough to meet specific needs in cities - like the topography of the roadways, daily amount of goods to deliver and the legal provision at the local situation. Production of LEV in small and medium enterprises will unlock a niche for first industrial uses of Natural Fiber Composites (NFC) in load-bearing structures. By pre-impregnation a replicable quality will bring the structural light-weight construction with NFC to new fields of use, as the construction of a LEV will demonstrate. At the end of its life cycle, the vehicle proves further economic and ecological benefits due to the use of NFC: A cost effective thermal conversion under a reduced release of fossil CO₂ is guaranteed. [3; 4]

Abstract: The present article addresses the evaluation of the electro-mechanical (E/M) impedance method as a Structure Health Monitoring (SHM) method to detect and classify damage, more specific, the debonding of a face layer.In the study the considered structure is simplified as a circular sandwich panel of constant thickness, consisting of isotropic face layers and a honeycomb core.The debonding is assumed to be circular and situated at the center of the panel, only variable in its radius.The article starts with a brief introduction to the basic idea of SHM and the fundamentals of the E/M impedance method.Further, the idealized setting is investigated by two sets of experiments whose results are analyzed by typically used damage metrics and by considering both analytical and numerical models.A coupled-field FEM model is developed and compared to the experimental results.Furthermore, an analytical model is derived to evaluate the experimental and numerical results.All results are presented and discussed extensively on pursuing the objective to detect and classify the size of a debonding.Finally, it is shown how a model based approach can predict the presence but also the size of a debonding in the considered sandwich panels based on the E/M impedance measurements.

Abstract: Conventional strain gauges made of constantan or CuCr for instance have a low value for structural health monitoring issues in plastic composites. These strain sensor materials exhibit small elastic regions and show fatigue when dynamically loaded with strain levels over 0.3 percent. For this reason, these sensors would break or fail before the composite life-time and thus cannot be integrated into this kind of composite materials. Pseudoelastic thermal shape memory alloys are therefore used as strain sensors and integrated into composites in order to allow piezoresistive strain measurement and structural health monitoring in such materials. Thermal treatments are used to create sensor structures out of shape memory alloy wires. Pseudoelastic shape memory wires can be strained up to 8 percent repeatedly. Their gauge factor is higher than 5. Shape memory strain sensors are successfully embedded into glass fibre reinforced plastics and show a significant and reproducible resistance change when the composite is strained. The dynamic strength is magnificently higher compared to conventional strain gauges. Shape memory strain sensors are an efficient alternative to fiber-bragg-grating sensors and can potentially be used for strain measurements in different plastics and textile materials. Shape memory sensor structures can be embedded or applied and are good candidates for structural characterisation and monitoring applications.