Award Date

1-1-2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Committee Member

Brendan J. O'Toole

Number of Pages

180

Abstract

The aim of this study is to analyze and assess the dynamic behavior of bolted joint connections subjected to impact loads using Finite Element Analysis (FEA) and experiment. Also, it investigates the effect of the joint on shock propagation through the structure. There is little or no literature available describing the proper method for analyzing the transient shock propagation across bolted connections. The main study will be performed on hat sections bolted to a flat plate. These simple configurations are representative of structures found in many military ground vehicles that can be subjected to transient impact and blast loads. The best way to approach this problem is first to compare and verify the experiment and modeling results on the plate and hat section individually. The next step is to verify the result of a bolted structure. The last step would be a parametric study of the bolted joints with different variables, such as contact type and area, friction, preload on bolt, vibration characteristics of bolt and spacers and FEA results output frequency; An impulse hammer with built in load cell along with accelerometers have been used to obtain the response of the shock for the experimental work. Finite element Method (FEM) is used for analysis. The model has been made and meshed in HyperMeshRTM, and then exported to LS-DYNA to solve and obtain the results from the shock applied to the structure; The results will be presented in three categories. First the modal analysis is performed both numerically and experimentally. The results were in excellent agreement with less than 2% error. Secondly, the time history response of FEA and experimental results are compared together. Different methods such as Root Mean Square (RMS), moment method and maximum peak acceleration method was used to obtain the resemblance of experimental and Finite Element responses. The results show that solid elements with a fine mesh must be used in the modeling the structure to obtain a reliable response from FEA. Finally, the Shock Response Spectrum (SRS) is used to calculate the critical frequency for design purposes. As long as the structure is modeled with the solid elements and mesh is refined properly the FEA and experiment detects the same critical frequency; The study of shock propagation through structure with bolted joints showed that joint is reducing the maximum acceleration amplitude by a factor of 3. Furthermore, using a washer and bolt with a lower stiffness material can attenuate shock significantly. In some cases there is up to 40% reduction in peak acceleration.

Keywords

Bolted; Bolted Joints; Element; Experimental; Finite; Joints; Shock; Shock Transmission; Studies; Transmission; Vibration Testing

Controlled Subject

Mechanical engineering

File Format

pdf

File Size

4280.32 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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