Optimization of a roll over protective structure (ROPS) using nonlinear finite element analysis

Abstract

Safety has become one of the major thrusts of our society. It is important in every facet of our lives. It is especially important in the agricultural industry. The use of a conventional Roll Over Protective Structure (ROPS) on farm tractors over the years has saved numerous lives and prevented countless injuries. Despite the added safety of using a ROPS, it has been found a percentage of tractor owners remove the conventional ROPS. One reason for removal is lack of a storage area to house the tractor with a conventional ROPS on it. The main reason deals with the ROPS becoming entangled with crops and limbs as it is being driven, sometimes even causing this debris to strike the tractor operator. By removing the ROPS, the tractor operators place themselves in unwarranted danger. This led the National Institute for Occupational Safety and Health (NIOSH) and West Virginia University Mechanical and Aerospace Engineering to the development of a deployable ROPS, which could remain down to aid in required housing space for the tractor and prevent debris from striking the tractor operator while being driven. This ROPS was tested for rapid deployment and also against the SAE J2194 Static Load Standard. The results of the SAE J2194 Static Load Standard tests revealed the ROPS was structurally over-designed. This research effort focuses on the application of computer-aided design and analysis to structurally optimize the deployable ROPS and make it lighter. The first objective deals with the development of a finite element model (FEM) of the original deployable ROPS giving analytical results that matched the experimental results. This justified the use of a FEM to optimize the ROPS. Once this was accomplished, a FEM of an optimized deployable ROPS was created and verified as safe by checking energy and deflection results against the SAE J2194 Static Load Standard. v TABLE OF CONTENTS ABSTRACT ii ACKNOWLEDGEMENTS iii TABLE OF CONTENTS v LIST OF FIGURES viii LIST OF TABLES x NOMENCLATURE xi CHAPTER 1 INTRODUCTION 1 1.1 Introductory Remarks 1 1.2 Review of Relevant Literature 3 1.3 Thesis Objective 8 CHAPTER 2 SAE J2194 ROPS STANDARD 9 2.1 Introduction 9 2.2 Energy Criteria 9 2.3 Accuracies and Tolerances CHAPTER 3 EXPERIMENTAL APPARATUS 17 3.1 Test Rig and Equipment 3.2 Data Acquisition 25 3.3 Data Acquisition Program CHAPTER 4 SOLID AND FINITE ELEMENT MODEL DESCRIPTIONS 4.1.1 Mechanical CAD Software 4.1.2 Modeling the Two Post Deployable ROPS vi 4.1.