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Research Papers

Simulation of Secondary Contact to Generate Very High Accelerations

[+] Author and Article Information
Stuart T. Douglas, Moustafa Al-Bassyiouni, Abhijit Dasgupta

Department of Mechanical Engineering,
University of Maryland,
College Park, MD 20742

Kevin Gilman, Aaron Brown

Lansmont Corporation,
17 Mandeville Ct,
Monterey, CA 93940

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received October 20, 2013; final manuscript received April 26, 2015; published online June 18, 2015. Assoc. Editor: Felix Chen.

J. Electron. Packag 137(3), 031011 (Sep 01, 2015) (8 pages) Paper No: EP-13-1121; doi: 10.1115/1.4030685 History: Received October 20, 2013; Revised April 26, 2015; Online June 18, 2015

This paper investigates the design of a typical commercially available drop system for generating very high shock and drop accelerations. Some commercially available drop towers produce accelerations greater than 5000 G by utilizing the dynamics of secondary impact, using an attachment termed a dual mass shock amplifier (DMSA). Depending on the design, some DMSAs are capable of repeatedly generating accelerations as high as 100,000 G. The results show that a finite element model (FEM) can capture the peak acceleration for the drop tower and the DMSA within 15%. In this paper, a detailed description of the test equipment and modeling techniques is provided. The effects of different design parameters, such as table mass, spring stiffness, and programmer material properties, on the drop profile, are investigated through parametric modeling. The effects of contact parameters on model accuracy are explored, including constraint enforcement algorithms, contact stiffness, and contact damping. Simple closed-form analytic models are developed, based on the basic principles of a single impact and the dynamics of secondary impact. Model predictions are compared with test results. Details of the test methodology and simulations guidelines are provided. Detailed finite element analysis (FEA) is conducted and validated against the experimental tests and compared to the simplified theoretical simulations. Benefits in exploring FEM to simulate contact between materials can be extrapolated to different architectures and materials such that with minimal experimental validation impact acceleration can be determined.

Copyright © 2015 by ASME
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References

Figures

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Fig. 1

Commercial drop tower with details marked

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Fig. 2

DMSA with details marked

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Fig. 3

Acceleration profiles of the drop table and DMSA table in a secondary impact test

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Fig. 4

Single degree-of-freedom (DOF) description of the initial (primary) impact between the drop table (including the DMSA base), M1, and the impact table, separated by a long, cylindrical, elastomer pulse shaper, K1

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Fig. 5

Two DOF model representing the secondary impact due to collision between the DMSA table (M2) and the drop table with the DMSA base (M1), separated by an elastomer sheet of stiffness, K2

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Fig. 6

Idealization of the displacement of the drop tower with the DMSA accessory during a drop test

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Fig. 7

Idealization of the velocity of the drop tower with the DMSA accessory during a drop test

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Fig. 8

Drop tower assembly model with DMSA and elastomer pulse shaping material used in the initial velocity model

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Fig. 9

Simple model FEA used to investigate contact stiffness and damping factors

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Fig. 10

Acceleration analysis of the critical damping fraction

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Fig. 11

Peak acceleration values as a function of the critical damping fraction derived from the single DOF model

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Fig. 12

Combined contact parameters

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Fig. 13

The effect of mass-proportional damping defined in the elastomer material on the initial impact of the drop table with the DMSA base

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Fig. 14

The effect of mass-proportional damping, α, of the elastomer material, on the secondary impact between the DMSA table and drop table

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Fig. 15

High-speed video capture of the drop table with the DMSA accessory. Left to right chronologically, after the initial impact, second impact of the DMSA table and the drop table with the DMSA base, and after the secondary impact.

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Fig. 16

Drop tower with the DMSA accessory FEA simulation screenshots. Left to right, top to bottom chronologically: just before the initial impact with the elastomer, during impact with the elastomer, and after the secondary impact between the tables.

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Fig. 17

FEA versus experimental acceleration during a 15 in. drop

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Fig. 18

FEA versus experimental velocity during a 15 in. drop

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Fig. 19

Peak acceleration values from the DMSA table with added mass during a 15 in. drop

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Fig. 20

Time to impact of DMSA and drop table

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