Award Date

5-1-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering

Department

Mechanical Engineering

First Committee Member

Mohamed B. Trabia

Second Committee Member

Brendan J. O'Toole

Third Committee Member

Woosoon Yim

Fourth Committee Member

Zhiyong Wang

Fifth Committee Member

Yi-Tung Chen

Sixth Committee Member

Rama Venkat

Number of Pages

185

Abstract

Understanding the transient behavior of structures with bolted joints when subjected to medium and high shock or impact loads can be challenging due to their nonlinear response, which is induced by the complex interactions between the bolts and the structure. While few researchers have considered shock transmission through bolted joints at low impact loading, there are little literature on shock transmission through bolted joints under high loading conditions. Low impact loading condition generally excites the lower order frequencies but under high impact loading higher order frequencies are excited. Typical factors that affect the response of a bolted joint include, preload (bolt tightening), intensity of the impact, and damping within the joint. The complexity in designing bolted joints under these conditions lies in the limitations of available methods to characterize their behavior.

The main objective of this work is to develop computational tools for predicting the shock transmission through bolted joints under medium and high impacts. Examples of these impacts are blast loading and projectile impact. The effect of tightening torque of the bolts on the response is also studied. The strain rate effect of the bolts due to high impact loading is also studied.

The study is done in two steps. The first step is a high impact study on a square flange system using a Two-stage gas gun. A steel plate is impacted using Lexan polycarbonate projectile at around 6 km/s. The impact surface is penetrated by the projectile on impact. The response acceleration is measured post joint. The second step would be to study medium impacts on a bolted connection using a circular fixture with a bolted lid to replicate a vessel. This structure is subjected to impact loading in a drop tower. The experiment is conducted at different pre-load torque for the bolts. The bolts are subjected to plastic deformation. The responses are measured using an accelerometer and a force sensor.

For these two cases, Finite Element Analysis (FEA) is performed. The bolts are modeled as solid elements. In both of these cases, strain rate effect is considered for both the structure and bolts. For high impact study using Two-stage gas gun, the impact region is modeled using Smooth Particle Hydrodynamic (SPH) technique and Lagrangian method is used for rest of the material.

The simulation and experimental results from both cases are compared using a combination of Fast Fourier Transforms (FFT) and Shock Response Spectrum (SRS).

Keywords

Bolted joints; Impact; Shock (Mechanics); Shock waves--Mathematical models

Disciplines

Mechanical Engineering

File Format

pdf

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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