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Now showing items 31-40 of 41
Aufsatz
Evaluation of extremely steep residual stress gradients based on a combined approach using laboratory-scale equipment
(2021-11-30)
Surface treatments characterized by rapid heating and cooling (e.g. laser hardening) can induce very steep residual stress gradients in the direct vicinity of the area being treated. These gradients cannot be characterized with sufficient accuracy by means of the classical sin2Ψ approach applying angle-dispersive X-ray diffraction. This can be mainly attributed to limitations of the material removal method. In order to resolve residual stress gradients in these regions without affecting the residual stress equilibrium, ...
Aufsatz
Laser welding of grey cast iron with spheroidal graphite-influence of process parameters on crack formationand hardness
(2021-03-24)
In the investigation at hand, sheets of ferritic and pearlitic grey cast iron with spheroidalgraphite are welded using a fiber-laser. The influence of varying laser power and welding speed onthe macroscopic characteristics of the weld seam and crack formation are analyzed and discussed.Substantial crack formation with crack densities of up to2.93 cm−1are found. Furthermore, hardnessmeasurements are conducted to evaluate the formation of brittle phases within the weld metaland heat-affected zone. Peak hardness values ...
Aufsatz
Identification of a Spatio-Temporal Temperature Model for Laser Metal Deposition
(2021-12-18)
Laser-based additive manufacturing enables the production of complex geometries via layer-wise cladding. Laser metal deposition (LMD) uses a scanning laser source to fuse in situ deposited metal powder layer by layer. However, due to the excessive number of influential factors in the physical transformation of the metal powder and the highly dynamic temperature fields caused by the melt pool dynamics and phase transitions, the quality and repeatability of parts built by this process is still challenging. In order to ...
Aufsatz
Actuation of an elastic membrane by the use of an electrorheological valve
(2021-01-25)
The dynamic response of a fluidic actuator is investigated on the basis of numerical simulations. With this actuator a membrane is excited to oscillate by means of an electrorheological valve. For this purpose the solid and fluid domains are coupled. Furthermore, the constitutive equation of the fluid is coupled to the electric field. The dynamic response is discussed on the example of a variable stiffness of the membrane. Actuators of this type offer the potential to delay the transition of a boundary layer.
Aufsatz
Simultaneous determination of Bingham material parameters using a ball probe concrete rheometer
(2021-01-25)
A new evaluation method allowing direct determination of the Bingham parameters from ball probe rheometers. A non‐linear relationship between the direct measured variables and the material parameters is revealed through numerical parameter studies. The method was validated on two devices of the ball probe type with different dimensions. Comparison with other methods showed good agreement. It is pointed out how the evaluation method can be transferred to devices having other dimensions by performing a limited number ...
Aufsatz
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
Damping based on electromagnetic induction: A comparison of different minimal models
(2021-01-25)
Damping of structural vibrations is a crucial part of modern engineering. Using electromagnetic interactions for this purpose is a modern and promising approach. To gain better understanding of phenomena involved in this technique investigations on minimal models of a B‐field modulation dampers are shown. Therefore two different setups are compared. One uses a permanent magnet as the source for the magnetic field, one uses a coil, respectively an electro‐magnet as the source. The contribution focuses on differences ...
Aufsatz
Derivation of Analytical, Closed‐form Formulas for the Calculations of Instantaneous Screw Axes of Arbitrary Rigid 3D Multi‐Body Systems
(2021-01-25)
A method to calculate the parameters for each instantaneous and relative instantaneous screw axis in an arbitrary rigid multi‐body system is presented. At first a kinematic analysis is performed which calculates the displacements of all nodes and the rotation of each body. In the next step the displacements of the nodes and the rotation of the bodies are used to calculate the instantaneous screw axis of each body. With the information on the instantaneous screw axes the instantaneous relative screw axes can be computed ...
Aufsatz
Measuring the Time Discretization Error in Linear Elasticity
(2021-01-25)
The present paper considers the spread of longitudinal waves in an elastic rod. On the one hand an analytical solution is presented, on the other hand a spatially and temporally discretized continuum formulation of this problem is treated. With these approaches at hand the appearing time discretization error is analyzed using various quantities.