Modeling of ultrasonic processes utilizing a generic software framework

Modeling of ultrasonic processes is typically characterized by a high degree of complexity. Different domains and size scales must be regarded, so that it is rather difficult to build up a single detailed overall model. Developing partial models is a common approach to overcome this difficulty. In this paper a generic but simple software framework is presented which allows to coupe arbitrary partial models by slave modules with well-defined interfaces and a master module for coordination. Two examples are given to present the developed framework. The first one is the parameterization of a load model for ultrasonically-induced cavitation. The piezoelectric oscillator, its mounting, and the process load are described individually by partial models. These partial models then are coupled using the framework. The load model is composed of spring-damper-elements which are parameterized by experimental results. In the second example, the ideal mounting position for an oscillator utilized in ultrasonic assisted machining of stone is determined. Partial models for the ultrasonic oscillator, its mounting, the simplified contact process, and the workpiece's material characteristics are presented. For both applications input and output variables are defined to meet the requirements of the framework's interface.DF

Reduced Order Modeling of Mistuned Bladed Disks under Rotation

In this paper, a substructure-based reduced order model for mistuned bladed disks is extended to account for the effect of rotational-dependent dynamic properties. To reduce the overall size of the structural model, successive transformations to reduced modal subspaces of smaller dimension are performed by means of a fixed-interface Component Mode Synthesis, a Wave-Based Substructuring, and a Secondary Modal Truncation. Since the threedimensionally shaped rotor blades tend to untwist under the influence of centrifugal forces, the modal reduction bases may undergo significant changes for different speeds of rotation. To prevent the necessity of identifying individual modal subspaces for each operating point and a repetitious passing through the full reduction process, a multi-model formulation is used to obtain a parameterized reduced order model in terms of rotational speed. The accuracy of this approach is assessed by comparison with full finite element models for various steady operating conditions. In terms of computational solution time, the proposed approach outperforms the finite element calculation by 90%. Finally, numerical results are presented addressing the mitigating influence of constant and variable rotational speeds on the amplitude amplification of mistuned bladed disks

Influence of the ultrasonic vibration amplitude on the melt pool dynamics and the weld shape of laser beam welded EN AW-6082 utilizing a new excitation system for laser beam welding

Laser beam welding is a commonly used technology for joining similar and dissimilar materials. In order to improve the mechanical properties of the weld, the introduction of ultrasonic vibration into the weld zone has been proposed [5]. The ultrasonic system consists of an electronic control, a power supply, a piezoelectric converter and a sonotrode, which introduces the vibration into the weld zone. Its proper design is of great importance for the process performance. Furthermore, the effects of ultrasound in a melt pool need to be understood to evaluate and optimize the process parameters. In addition, it is important to find out the limits of ultrasonic excitation with respect to a maximum vibration amplitude. Therefore, firstly different methods of ultrasonic excitation are investigated and compared with respect to their performance. A system which is based on using longitudinal vibrations turns out to be the best alternative. Secondly, the system design is described in detail to understand the boundary conditions of the excitation and finally, simulations about the influence of ultrasonic vibrations are done by using a simplified model. The system is used to perform experiments, which aim at detecting the maximum vibration amplitude doing bead on plate welds of EN AW-6082 aluminum alloy. The experiments reveal a significant change of the weld shape with increasing ultrasonic amplitude, which matches the simulative findings. If the amplitudes are small, there is a marginal effect on the weld shape. If the amplitudes are high, melt is ejected and the weld shape is disturbed. In the present case, amplitudes over 4 µm were found to disturb the weld shape. © 2021, The Author(s)

Investigations on the effect of post treatment utilizing ultrasonic standing waves on the hardness of laser beam welds in stainless steel

Laser beam welding is precise, quick and highly automatable. Nevertheless, disadvantageous hardness profiles can result and promote cracking. By an ultrasonic post treatment, crystal defects, internal stress and grain structure can be altered to achieve uniform hardness. In the investigations round bars with 30 mm diameter made from stainless steel grade 1.4301 are welded by laser in a rotational process. Ultrasonic excitation is applied utilizing a longitudinal mode of the system. The weld pool is positioned in the node or the antinode of the amplitude distribution. The excitation amplitude varies at 0/2/4 µm and the treatment durations at 0/5/10 min. The welds are evaluated by metallographic cross sections and hardness measurements. The results indicate the effects of acoustic residual softening and hardening. With standard deviations of about 2 %, the weld hardness is decreased by 3 % with nodal excitation and increased by 4 % with antinodal excitation. The difference between weld and base material hardness is not reduced since the base material is hardened at all ultrasonic parameters used

Forced response of turbine bladings with alternating mistuning and friction damper coupling

Alternating mistuning of blades can help to avoid aerodynamic instabilities of turbine bladings. The influence of this type of intentional mistuning on the design of friction dampers has hardly been explored so far. To investigate the dynamics of alternately istuned and nonlinearly coupled bladed disks a simple model is set up. The structure is represented by a plane lumped mass cyclic sector model with a single DOF oscillator for each blade. Underplatform dampers, referred to as friction dampers, are considered in terms of separate rigid bodies. Contact forces are evaluated by a penalty-based point contact model. Forced response functions and damper optimization curves are computed and show the potential of improved friction damping performance due to mistuning