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End date: 2024 × Start date: 2020 × Type: article × Version: acceptedVersion × Publisher: Amsterdam [u.a.] : Elsevier ×

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Now showing 1 - 3 of 3
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    Development and Implementation of a Guideline for the Combination of Additively Manufactured Joint Assemblies with Wire Actuators made of Shape Memory Alloys
    (Amsterdam [u.a.] : Elsevier, 2023) Löffler, Robin; Tremmel, Stephan; Hornfeck, Rüdiger
    Smart Materials actuators in the form of wires made of shape memory alloys in combination with additively manufactured carrier components are used in a wide variety of prototype developments of innovative joint assemblies. This combination is relevant because of the same manufacturing costs of the additively manufactured components, which are independent of the quantity of parts, the free geometric design possibilities as well as the huge energy density of the aforementioned actuator technology. In particular, the focus is on the possibility of appropriately fitting large wire lengths on a compact part volume while taking into account acceptable force losses. Since there is no design guideline for such joint developments, each is individual, which results in unnecessarily long development times and a higher risk of errors. Based on selected in-house and third-party examples, integration possibilities of shape memory alloy wire actuators in additively manufactured carrier components are analysed and transferred into a universally applicable design guideline. These recommendations are brought into the framework of existing design guidelines of the VDI (Verein Deutscher Ingenieure – Association of German Engineers), namely VDI 2206 and VDI 2221 with extensions for additive manufacturing, for a better usability and integrability into existing processes. Finally, this results in a simplified access to the topic of the combination of additive manufacturing and shape memory alloys and a more efficient realisation of such joint developments.
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    Geometric Basics and Calculation Methods for the Design of a Technical Saddle Joint based on Owl Neck Vertebrae
    (Amsterdam [u.a.] : Elsevier, 2023) Gründer, Johannes; Hornfeck, Rüdiger
    A saddle joint enables the movement of two components relative to each other primarily about two axes of rotation and, to a limited extent, in translational direction. This type of joint is primarily found in nature, for example in the human thumb, in the ossicles and the cervical spine of owls. Motivated by the high degree of the owls’ head mobility, the authors aim to make this high motion potential technically accessible by defining relevant design parameters and developing calculation methods for dimensioning the saddle joint components. First, an abstracted contact geometry model based on the owls’ saddle joints is de-fined. A method for calculating the kinematics of the joint as a function of the previously introduced design parameters of the contact is derived mathematically. Regarding the implementation in a design process, this model is used to calculate the restoring forces required to stabilize the joint parts as well as the actuator torque needed for a specific rotational movement around those axes. Furthermore, the rotational stiffness of a specific joint geometry is calculated as an important design criterion. In summary, the defined contact geometry, the kinematics, and the computable forces serve as basis for designing technical saddle joints in the future.
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    Electrically conductive and piezoresistive polymer nanocomposites using multiwalled carbon nanotubes in a flexible copolyester: Spectroscopic, morphological, mechanical and electrical properties
    (Amsterdam [u.a.] : Elsevier, 2022) Dhakal, Kedar Nath; Khanal, Santosh; Krause, Beate; Lach, Ralf; Grellmann, Wolfgang; Le, Hai Hong; Das, Amit; Wießner, Sven; Heinrich, Gert; Pionteck, Jürgen; Adhikari, Rameshwar
    Nanocomposites of multiwalled carbon nanotubes (MWCNTs) with poly(butylene adipate-co-terephthalate) (PBAT), a flexible aromatic–aliphatic copolyester, were prepared by melt mixing followed by compression moulding to investigate their spectroscopic, morphological, mechanical and electrical properties. A comparison of the Fourier transform infrared (FTIR) spectra of the neat polymer matrix and the composites showed no difference, implying a physical mixing of the matrix and the filler. A morphological investigation revealed the formation of a continuous and interconnected MWCNT network embedded in the polymer matrix with partial agglomeration. Increasing Martens hardness and indentation modulus and decreasing maximum indentation depth with increasing filler concentration demonstrated the reinforcement of the polymer by the MWCNTs. A volume resistivity of 4.6 × 105 Ω cm of the materials was achieved by the incorporation of only 1 wt.-% of the MWCNTs, which confirmed a quite low percolation threshold (below 1 wt.-%) of the nanocomposites. The electrical volume resistivity of the flexible nanocomposites was achieved up to 1.6 × 102 Ω cm, depending on the filler content. The elongation at the break of the nanocomposites at 374% and the maximum relative resistance changes (ΔR/R0) of 20 and 200 at 0.9 and 7.5% strains, respectively, were recorded in the nanocomposites (3 wt.-% MWCNTs) within the estimated volume resistivity range. A cyclic strain experiment shows the most stable and reproducible ΔR/R0 values in the 2%–5% strain range. The electrical conductivity and piezoresistivity of the investigated nanocomposites in correlation with the mechanical properties and observed morphology make them applicable for low-strain deformation-sensing.