Extracting fixed base modal models from vibration tests on flexible tables.
a acceleration dof degree of freedom H Frequency response function f Applied force FE Finite Element FRF Frequency Response Function Φc The mode shape matrix of the bare table at dof to be constrained Subscripts c degree of freedom at locations to be constrained f dof at free locations t dof at tip of the slip table s dof at the classic shaker input location on the slip table i any other dof not including t or s
Measuring Effective Mass of a Circuit Board
Effective mass is a system property of a base mounted structural mode of vibration in a specific system axis. Effective mass is usually calculated with the finite element model. A method of deriving effective mass from dynamic measurements on the hardware was presented previously. The method is applied to a circuit board mounted on a fixture for the out of plane axis. The uncertainty of the method is evaluated using a nylon plate truth model of about the same dimensions and weight as the circuit board. The method measures frequency response functions on the fixture supporting the circuit board. Modes are extracted, and the mode shapes are processed to estimate the effective mass of each fixed base mode. These results will ultimately be used to support energy based failure analysis on the circuit board.
Receptances of non-proportionally and continuously damped plates—Reduced dampers method
Abstract This paper presents a method for the dynamic analysis of continuously and non-proportionally damped plates in bending modes. The damping can be in the form of constrained or unconstrained layers. The method is an extension of the equivalent dampers method discussed in a previous paper, in which the damping matrix of a discretized plate is replaced by a diagonal equivalent damping matrix. Each diagonal element represents an equivalent damper inserted between the structure and ground. In this method the number of equivalent dampers is reduced so that the receptance matrix of the damped structure can be obtained economically by a direct matrix method. The receptances of two different partially coated plates in transverse directions are computed by the method suggested. The verification of the results is demonstrated by comparison with the experimental values and also with the theoretical values obtained by the equivalent dampers method. The method presented can also be applied to the transverse vibration analysis of plates with discrete damping inserts.