Lightweight Design New Shaker Design with Accelerations up to 1000g
Researchers at the Fraunhofer Institute for Structural Durability and System Reliability LBF are taking components to their limits using resonance superelevation tests. Using a new type of test setup, they can excite components harmonically monofrequentially with much higher accelerations than before.
Components must be able to withstand extreme loads. High accelerations can occur especially in electronic components that are installed near fast-rotating electric motors. At Fraunhofer LBF, test objects can be tested by means of resonance superelevation tests with more than ten times higher accelerations than with a conventional shaker setup. This is made possible by the broad positioning of the Fraunhofer LBF in the fields of environmental simulation, fatigue strength, numerical simulation and individual complex component manufacturing. In their test setup, the scientists at the Darmstadt Institute extend a shaker by a resonance setup, which makes it possible to operate the system and the test object in resonance at a desired frequency. In addition, the forces acting on the test apparatus are kept low by lightweight design of the moving masses. In this way, the researchers can achieve accelerations of up to 1000g with a harmonic excitation with comparatively little effort.
Precise Design through Numerical Simulation
For the optimal design of the overall structure, the LBF team carries out a numerical simulation in advance. In this way, various parameters of the structure can be precisely estimated, which are decisive for the resonance frequency. Thomas Pfeiffer, who is in charge of the test setup at Fraunhofer LBF, emphasizes what is special about this: "As a provider of environmental simulations in the department, we can rely on a group that deals with numerical analyses. If necessary, we can also validate the numerical model experimentally using the individual set-up". The simulation then allows the load on the individual test setup components to be estimated in advance. This ensures that the desired test duration can be achieved. In a validation experiment, the researchers can further improve the simulation and estimate the maximum possible excess acceleration over the maximum acceleration of the shaker.
Excitation in Resonance
Many years of experience in the field of dynamic load application enable Fraunhofer LBF to design moving parts precisely and in accordance with the requirements for the respective loads. With the help of its own laser sintering system, the institute can design complex parts of the resonance structure as a monolithic block. This saves weight and thus reduces the load on the shaker. The load capacity of the resonant test setup is also increased. "For the harmonic excitation of the test specimen, we can maintain a fixed frequency at the required acceleration or impose a maximum acceleration amplitude with frequency tracking within specified limits, depending on the customer's requirements," explains Pfeiffer.
Test Setup in Lightweight Construction
Depending on the application and use of the component to be tested, excitation accurate to one Hertz over a high number of oscillation cycles may be required. By numerical pre-design, lightweight design and resonance build-up, these requirements can be implemented on the test bench. The acceleration amplitude is controlled according to the specifications of the test object. It is also possible to excite a maximum acceleration in resonance at a slightly variable frequency by tracking the frequency. The focus of the test here is on the high acceleration amplitude with which the component is to be loaded. C. & E. Fein GmbH has already tested the new test possibilities in practice. "Thanks to the interaction of various specialist disciplines at the Fraunhofer LBF, it is possible to design test specifications according to our wishes, to exhaust existing testing machines and to test outside of standard specifications. The close solution-oriented cooperation allows objectives to be adapted and implemented according to the situation", says Dr. Mark Heilig, responsible for Technical Analysis/Systems analysis at C.& E. Fein GmbH.