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M.S. Thesis Defense – R. Sridharan

Title: Stress Response of Tall and Heavy Electronic Components Subjected to Multi-axial Vibration

Day: February 24, 2017

Time: 10:30am

Location: EGR 2164

Committee:

Professor Abhijit Dasgupta

Professor Miao Yu

Professor Amr Baz

Abstract:

Electronic assemblies often experience multiaxial vibration environments in use and tall, heavy components are more vulnerable to such multiaxial vibration than are shorter, lighter assemblies.  The added vulnerability comes from higher stresses that are a result of nonlinear dynamic amplification which large components are susceptible to under simultaneous multiaxial excitation, termed multi degree of freedom (MDoF) excitation.  However, it is still common practice to conduct vibration durability testing on electronic assemblies one axis  at a time – in what is termed sequential single degree of freedom (SSDoF) testing.  SSDoF testing has been shown to produce lower fatigue damage accumulation rates than simultaneous MDoF testing, in the leads of tall and heavy electronic components.  This leads to overestimating the expected lifespan of the assembly.

This paper investigates the geometric nonlinearities and the resulting cross-axis interactions that tall and heavy electronic components experience when subjected to vibration excitation along two orthogonal axes – one direction is in the plane of the PWB and the other is along the normal to the PWB.  The direction normal to the PWB aligns with the axial direction of the leads, while the in-plane direction aligns with the primary bending direction of the leads.  Harmonic excitation was simultaneously applied to both axes to study the vibration response as a function of: frequency ratio, phase difference and amplitude of the excitation along the two axes.    The experimental observations were verified with a nonlinear dynamic Finite Element study.  The effect of geometric nonlinearity on cyclic stresses seen in the vibrating component are analyzed.