Effect of Matching Buckling Loads on Post-Buckling Behavior in Compliant Mechanisms

In this paper, a novel method for stiffness compensation in compliant mechanisms is investigated. This method involves tuning the ratio between the first two critical buckling loads. To this end, the relative length and width of flexures in two architectures, a stepped beam and parallel guidance, are adjusted. Using finite element analysis, it is shown that by maximizing this ratio, the actuation force for transversal deflection in post-buckling is reduced. These results were validated experimentally by identifying the optimal designs in a given space and capturing the force-deflection characteristics of these mechanisms.

Design and simulation of an out-of-plane electrothermal microactuator

Microactuators are one of the most important components in microelectromechanical systems (MEMS). Therefore, designing effective out-of-plane actuators has been in progress for the last decade. This paper presents a novel design of the microactuator with a double stepped beam structure for large out-of-plane deflection output applied to microvalves. The design and analysis of the out-of-plane microactuator are implemented by the finite element method. Silicon is selected as the material of the actuator and the beam motion is generated by the Joule heating effect. Compared to a single stepped beam design reported in the literature, the simulation results show that the proposed double-stepped beam structure can deliver a much larger out-of-plane deflection. Under an applied current of 15 mA, the maximum deflection of the double stepped beam is nearly seven times higher than that of the single stepped beam structure. In addition, the stress analysis indicates that the largest stress (1.46 GPa) induced in the beam is much smaller than the yield strength (7 GPa) of the selected silicon material.

The Collapse Analysis of the Lateral-Torsional Buckling of I-Shaped Stepped Steel Beams

The use of a non-prismatic member such as a stepped beam as a design method has the ability to function as a tool for steel beams optimization. A cover plate is partially welded on the upper and lower flange of the member at the maximum bending moment location to increase its flexural strength and, under critical load, flexural members bend about its strong axis, displace to the lateral direction, and twist coincidentally through a phenomenon known as the Lateral-Torsional Buckling (LTB). There is, however, no equations in the AISC 360-16 specification to calculate the critical moment of a stepped beam (Mst). Therefore, this research focuses on developing Mst for a simply supported stepped beam which deforms on its shear center under static-transverse loading through the use of a collapse analysis and the behavior of the beam. The results showed the welded cover plates consequently increased the LTB resistance of the prismatic I-shaped steel beam from 9.8% to 202% while the critical moment increased more significantly with an increment in the ratio of the cover plate length to the unbraced length (α). The cover plate thickness was observed to have dominantly affected only a large α ratio while the post-buckling characteristic of large α showed a sudden collapse phenomenon. Furthermore, the LTB modification factor was generated in this study due to the initial geometrical imperfection from the first mode of Eigen shape with maximum amplitude Lb/2000 (Cb1) and stepped beam shape (Cst) which were required to estimate the critical moment of a stepped beam based on the AISC equation for a prismatic beam.