| Vibration & Fatigue Analysis |
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The vibration behavior of a structure which is subjected to dynamic forces can be predicted using finite element analysis (fea) modeling. The manner in which the structure behaves is determined by its stiffness, mass, damping, and constraints and it is important to determine this response since internal, oscillating stresses may exceed the strength or fatigue life of the material. Aircraft Designs (ADI) will set up a detailed finite element model of the structure and perform a static analysis first to make certain that the model represents the actual structure. Then a modes analysis is performed to determine the eigenvalues (natural frequencies) and mode shapes (eigenvectors) of the structure. Now, the model can be subjected to transient dynamic loads and or displacements to determine the time histories of nodal displacements, velocities, accelerations, stresses and reaction forces. A sin sweep analysis, a random vibration analysis, and a shock spectrum analysis can also be performed by ADI. Random vibration is of prime concern because all vehicles (cars, trucks, trains) traveling over a relative rough surface are subjected to this source of vibration and stress. Aircraft, missiles, and rockets are subjected to random vibration excitation. This is due to the extreme turbulence of jet exhaust downstream of the jet and rocket engines, and aerodynamic buffeting. The Root Mean Square (RMS) response is determined from the Power Spectral Density (PSD). The 3 sigma stresses from the RMS response are compared to the ultimate strength of the material to assure that the structure or component will not fail. The output from the Random vibration analysis can be interfaced with the fatigue/fracture analysis to estimate the durability of a structure. Knowing the load history, the fatigue analysis; the crack initiation and crack propagation time is predicted. The load history is the number of cycles and the dynamic responses of the structure over its intended service life. Knowing the load history, ADI can predict if a structure or component will meet its design service life. Aircraft Designs can also perform steady state and transient thermal analysis on printed circuit boards (pcb) and determine the case and junction temperatures of electronic components subjected to conduction, convection, and radiation. The temperature of pcb components is essential to the life and performance of the components. |
