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Experimental investigations of viscoelastic and ferroelectric heating in PZT–5H
(2021-01-25)
This contribution focuses on the separation of two effects causing a temperature change in experiments with electrically loaded ferroelectrics. These materials are often subjected to cyclic loading, where viscoelasticity prevails at lower electric fields, whereas dissipative heating by domain switching governs the heating above the coercive field. Different frequencies and load amplitudes are investigated experimentally.
Aufsatz
Extension of Gap Bridgeability and Prevention of Oxide Lines in the Welding Seam through Application of Tools with Multi-Welding Pins
(2021-07-30)
Friction stir welding has become important in many areas of production and is increasingly used for joining aluminum components. For long welding seams, conventional tools with only one welding pin reach their technical limitations due to low gap bridgeability. When welding aluminum, the stirred in surface layers, such as oxides, lead to a decrease in static and dynamic strength since linear accumulations are formed in the welding seam. The aim of the present study is to increase the gap bridgeability using tools ...
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On the appearance of horseshoe chaos in a nonlinear hysteretic systems with negative stiffness
(2021-09-16)
The problem of inhibition of horseshoe chaos in a nonlinear hysteretic systems using negative stiffness is investigated in this paper. The Bouc–Wen model is used to describe the force produced by both the purely hysteretic and linear elastic springs. The analytical investigation of the Hamiltonian shows that the appearance of separatrix in the system is directly related to the parameters of the hysteretic forces. This means that the transverse intersection between the perturbed and unperturbed separatrix can be ...
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Damage modelling for the lifetime prediction of structural adhesive joints subjected to hygro‐thermo‐mechanical long‐term loading
(2021-01-25)
A damage model is presented for the lifetime prediction of structural adhesive joints under hygro‐thermo‐mechanical loading. The damage approach is applied through a cohesive zone model together with the concept of effective stress. It consists of a temperature‐dependent creep and hygro damage evolution due to mechanical loading and chemical aging, caused by the local water concentration. The creep damage part considers multiaxiality of the loading by an equivalent stress. The model parameters are identified by means ...
Aufsatz
On A Hybrid Concept for Approximating Self‐Excited Periodic Oscillations of Large‐Scaled Dynamical Systems
(2021-01-25)
Concerning the approximation of self‐excited periodic oscillations in large‐scaled mechanical systems involving strong nonlinearities, this contribution suggests a concept for an efficient treatment. The presented Hybrid FD‐HB method takes the advantages of both schemes Harmonic Balance and Finite Difference to enhance the ratio of computational cost and accuracy for mechanical systems with many degrees of freedom. Within this contribution the residual equations, required when applying a NEWTON‐RAPHSON‐scheme, are ...
Aufsatz
Durability Properties of Ultra-High Performance Lightweight Concrete (UHPLC) with Expanded Glass
(2021-10-05)
It is important to ensure the durability and safety of structures. In the case of newly developed materials that are outside the current rules, it is important to investigate all aspects of structural safety. The material studied in the following is a structural lightweight concrete with an ultra-high-performance matrix and expanded glass as a lightweight aggregate. The material, with a compressive strength of 60–100 MPa and a bulk density of 1.5–1.9 kg/dm³, showed high capillary porosities of 12 vol% (ultra-high-performance ...
Aufsatz
Use of Design of Experiments (DoE) to Model the Sulphate Agent Amount of (Ultra)Finely Ground and Fast Hardening Portland Cement Clinker
(2021-09-25)
This paper presents a model to calculate the sulphate agent amount and sulphate agent ratio for fine grounded and fast hardening Portland cement clinker. Despite sufficient knowledge about the influence of calcium sulphate on the hydration process of cement, the sulphate agent amount is mostly adjusted empirically. As a result, often a wide and unfeasible experimental matrix has to be tested. In this work, Design of Experiments (DoE) was used in combination with in-situ X-ray diffraction (XRD) tests to accurately ...
Aufsatz
Laser Powder Bed Fusion Processing of Fe-Mn-Al-Ni Shape Memory Alloy—On the Effect of Elevated Platform Temperatures
(2021-01-20)
In order to overcome constraints related to crack formation during additive processing (laser powder bed fusion, L-BPF) of Fe-Mn-Al-Ni, the potential of high-temperature L-PBF processing was investigated in the present study. The effect of the process parameters on crack formation, grain structure, and phase distribution in the as-built condition, as well as in the course of cyclic heat treatment was examined by microstructural analysis. Optimized processing parameters were applied to fabricate cylindrical samples ...
Aufsatz
Full-scale testing of adhesively bonded timber-concrete composite beams
(2021-09-07)
This paper presents new findings on adhesively bonded timber-concrete composites with prefabricated concrete parts. Hereby, timber and concrete are bonded solely with adhesive and no metallic connectors have been used. Because the achievement of a continuous bond proved to be a critical point in past studies, special attention is given to that issue. The application procedure of the adhesives is investigated in small-scale bond samples and the manufacturing process in full-scale composite beams with a span of 8 m and ...
Aufsatz
Recent Developments in the Field of Modified Patankar-Runge-Kutta-methods
(2021-12-14)
Modified Patankar-Runge-Kutta (MPRK) schemes are numerical one-step methods for the solution of positive and conservative production-destruction systems (PDS). They adapt explicit Runge-Kutta schemes in a way to ensure positivity and conservation of the numerical approximation irrespective of the chosen time step size. Due to nonlinear relationships between the next and current iterate, the stability analysis for such schemes is lacking. In this work, we introduce a strategy to analyze the MPRK22(α)-schemes in the ...