MODELING AND SIMULATION OF SHOCK AND DROP LOADING FOR COMPLEX PORTABLE ELECTRONIC SYSTEMS
Askari Farahani, Alex Farbod
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In this study, the transient response of electronic assemblies to mechanical loading encountered in drop and shock conditions are investigated. Many manufactures face design challenges when evolving new designs for high strain-rate life-cycle loading. Examples of high strain-rate loading include drop events, blast events, vibration, ultrasonic process steps, etc. New design iterations invariably bring new unexpected failure modes under such loading and costly trial-and-error design fixes are often necessary after the product is built. Electronics designers have long sought to address these effects during the design phase, with the aid of computational models. However, such efforts have been difficult because of the nonlinearities inherent in complex assemblies and complex dynamic material properties. Our goal in this study is to investigate the ability of finite element models to accurately capture the transient response of a complex portable electronic product under shock and drop loading. The portable electronic assembly in this study consists of a circuit card assembly in a plastic housing. Dynamic loading, consisting of broad-band vibration tests and shock tests on an electrodynamic shaker, and drop tests on a commercial drop-tower are applied to the test system as well as to its constituent sub-assemblies. The tests at the sub-assembly level are used to calibrate the dynamic response of the individual constituents. The nonlinear interactions due to dynamic contact between these sub-assemblies are then investigated through shock and drop testing at the system level. Finite element models of the system are generated and calibrated at the subsystem level with results of random vibration and shock tests. The contact mechanics are then parametrically investigated with the finite element model by comparing with the drop response of the full product. The parametric study consists of sensitivity studies for different ways to model soft, non-conservative contact, as well as structural damping of the sub-assembly under assembly boundary conditions. The long-term goal of this study is to demonstrate a systematic modeling methodology to predict the drop response of future portable electronic products, so that relevant failure modes can be eliminated by design iterations early in the design cycle.