Reliability based design optimization of an articulating rod
Objective
Introduction
Results
The rod is then optimized to achieve minimum weight and higher reliability. After optimization, the reliability of the structure is found to be 0.8619 with a weight of 0.155
kg.
Articulating rod is an important member (link) in a slider crank mechanism. It is the link which converts the rotating motion of the crank to a corresponding reciprocating motion of the piston, or vice versa. The rod is subjected to high compressive stresses during its operation. Hence there is a necessity to design the rod to withstand these stresses based on various criteria to ensure that the yield stress generated within the bar does not exceed the material strength. It has to be noted that there are many other failure modes of the rod but this is the most significant mode of failure. While most of the rods are made of Aluminium, there are various factors affecting the stress generated within the rod. Three factors are considered in this project (for simplicity) and in precise, they are, the diameter of piston end, the load acting on the rod and the rod length. The rod is modeled and simulated using FEM software to compute the stress generated for different combinations of the variables and the one which has a greater influence on stress is obtained. A nonlinear limit state function is obtained using two point function approximation which approximates the stress generated within the rod. The reliability is then calculated using Hasofer-Lind Rackwitz and Fiessler (HLRF) method and Monte Carlo Simulation and checked for agreement. The rod is then optimized to achieve a greater reliability by modifying the defined random variables. While optimizing, it is ensured that the science and practicality of the problem is not sacrificed for reliability.
Reliability analysis has been done on the articulating rod to ensure that it does not fail while in operation. The articulating rod is initially designed with three independent random variables with three different distributions. The design of the rod is then modified based on the reliability of the rod against yielding. Two different methods to compute reliability is used. Two point function approximation is used to come up with a function for the von misses stress acting on the rod using which a non-linear problem specific limit state function is obtained. The rod is then optimized to achieve a maximum practical reliability.