Two-Step Design of Multicontact-Aided Cellular Compliant Mechanisms for Stress Relief

2012 ◽  
Vol 134 (12) ◽  
Author(s):  
Vipul Mehta ◽  
Mary Frecker ◽  
George A. Lesieutre
Keyword(s):  
Compliant Mechanisms ◽  
Effective Properties ◽  
Compliant Mechanism ◽  
Stress Relief ◽  
Homogenization Method ◽  
Computationally Efficient ◽  
Cellular Mechanisms ◽  
Linear Elastic ◽  
Step Procedure ◽  
Contact Mechanism

A methodology for topology optimization to the design of compliant cellular mechanisms with and without internal contact is presented. A two-step procedure is pursued. First, a baseline noncontact mechanism is developed and optimized via an inverse homogenization method using the “solid isotropic material with penalization” approach. This compliant mechanism is optimized to yield specified elasticity coefficients, with the capability to sustain large effective strains by minimizing local linear elastic strain. In the second step, a system of internal contacts is designed. The initial continuum model of a noncontact mechanism is converted into a frame model, and possible contact links are defined. A computationally efficient algorithm is employed to eliminate those mechanisms having overlapping contact links. The remaining nonoverlapping designs are exhaustively investigated for stress relief. A differential evolution optimizer is used to maximize the stress relief. The results generated for a range of specified elasticity coefficients include a honeycomb-like cell, an auxetic cell, and a diamond-shaped cell. These various cell topologies have different effective properties corresponding to different structural requirements. For each such topology, a contact mechanism is devised that demonstrates stress relief. In one such case, the contact mechanism increases the strain magnification ratio by about 30%.

Topology Optimization of Contact-Aided Compliant Cellular Mechanisms

2009 ◽  
Author(s):  
Vipul Mehta ◽  
Mary Frecker ◽  
George A. Lesieutre
Keyword(s):  
Topology Optimization ◽  
Contact Structure ◽  
Compliant Mechanism ◽  
Local Strain ◽  
Homogenization Method ◽  
Second Step ◽  
Cellular Mechanisms ◽  
Step Procedure ◽  
Contact Mechanism ◽  
The Continuum

Applications of topology optimization to design compliant cellular mechanisms with and without a contact mechanism are presented in this paper. A two-step procedure is developed. For cellular structures without contact, the inverse homogenization method is employed using ‘Solid Isotropic Material with Penalization’ approach. The compliant mechanism is optimized to yield prescribed elasticity coefficients. The structure is also required to undergo a large overall strain without exceeding the allowable local strain. Results including a honeycomb similar structure and a negative Poisson’s ratio structure are presented. To implement a contact mechanism in the second step, the continuum model of a non-contact structure is converted into a frame model. Such a model is investigated for a contact pair which would reduce the maximum local strain. The scheme demonstrates that stress relief can be obtained.

Stress Relief in Contact-Aided Cellular Compliant Mechanisms

2008 ◽  
Author(s):  
Vipul Mehta ◽  
Mary Frecker ◽  
George Lesieutre
Keyword(s):  
Compliant Mechanisms ◽  
High Strain ◽  
Stress Relief ◽  
Cellular Structures ◽  
Morphing Aircraft ◽  
Fracture Failure ◽  
Global Strain ◽  
Aircraft Skin ◽  
Structural Mass ◽  
Contact Mechanism

Cellular structures with an internal contact-mechanism are investigated. These contact-aided compliant mechanisms are shown to reduce the local tensile stresses, thereby providing additional global strain before yielding or fracture failure compared to honeycomb or auxetic cellular structures. An analytical model for such structures is developed and it is validated using FEA simulations. Two different materials are considered for comparison. More than 100% improvement in global strain capability is possible using the contact. A high-strain morphing aircraft skin is examined as an application of these mechanisms. The contact-aided cellular compliant mechanisms are more advantageous in terms of both the structural mass as well as the global strain compared to a non-contact design. In the application considered the stress-relief mechanism increased the global strain capability by as high as 37%.

Multivariate Parameter Sets for Optimal Synthesis of Compliant Mechanisms

2005 ◽  
Author(s):  
Alexander Shibakov ◽  
Stephen L. Canfield ◽  
Patrick V. Hull
Keyword(s):  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Mesh Size ◽  
Synthesis Process ◽  
Design Parameters ◽  
Control Points ◽  
Computationally Efficient ◽  
Alternative Approach ◽  
Multivariate Parameter ◽  
Simple Mapping

This paper will propose the use of control maps along with discretized elements or meshes in the design parameter set for optimizing compliant mechanisms. The use of control maps will be demonstrated to encode the motion of groups of nodes or control points defining the mesh with simple mapping rules. The technique will serve as an alternative to increased mesh size or node wandering techniques that have been proposed to increase the number of alternative design shapes that may be considered. As an alternative approach, the proposed control map parameterization has the significant benefit that it minimizes the number of design parameters necessary (parameters increase linearly with the mesh size) in describing a given design making it computationally efficient. A limited number of tiles can produce a map that has a significant effect on the final shape. If the tiles are chosen appropriately, the problems such as material overlap and non-convex mesh elements are avoided automatically. This paper will describe the implementation of these control maps and provide several examples showing their implementation in the compliant mechanism topology synthesis process.

Design of Bend-and-Sweep Compliant Mechanism for Passive Shape Change

2012 ◽  
Author(s):  
Yashwanth Tummala ◽  
Mary Frecker ◽  
Aimy Wissa ◽  
James E. Hubbard
Keyword(s):  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Shape Change ◽  
Stress Relief ◽  
Von Mises Stress ◽  
Nonlinear Stiffness ◽  
Compliant Joints ◽  
Stiffness Properties ◽  
Von Mises ◽  
Wing Morphing

Contact aided compliant mechanisms are a class of compliant mechanisms where parts of the mechanism come into contact with one another during motion. Such mechanisms can have nonlinear stiffness, cause stress-relief, or generate non-smooth paths. New contact aided compliant mechanisms called bend-and-sweep compliant mechanisms are presented in this paper. These bend-and-sweep mechanisms are made up of compliant joints which are alternately located in two orthogonal directions, and they also exhibit nonlinear stiffness in two orthogonal directions. The stiffness properties of these mechanisms, in each direction, can be tailored by varying the geometry of the compliant joints. One application of these mechanisms is in the passive wing morphing of flapping wing UAVs or ornithopters. A design study is conducted to understand the effect of hinge geometry on the deflections and maximum von Mises stress during upstroke and downstroke. It is shown that the bend-and-sweep compliant elements deflect as desired in both the bending and sweep directions.

Multi-scale failure analysis of plain-woven composites

2012 ◽  
Vol 47 (6) ◽  
pp. 379-388 ◽  
Author(s):  
Omar Bacarreza ◽  
MH Aliabadi ◽  
Alfonso Apicella
Keyword(s):  
Damage Mechanics ◽  
Effective Properties ◽  
Progressive Failure ◽  
Continuum Damage Mechanics ◽  
Internal Variable ◽  
Homogenization Method ◽  
Woven Composites ◽  
Computationally Efficient ◽  
Efficient Manner ◽  
Multi Scale

A numerical model capable of dealing with progressive degradation of plain woven composites in a computationally efficient manner is presented in this article. A semi-analytical homogenization method is used to derive effective properties of the composite from the material properties of the constituents. The progressive failure is described using nonlocal continuum damage mechanics where the driving internal variable for the damage is the nonlocal strain. The model was implemented into Abaqus/Explicit, where the failure of a longitudinal tension and an open hole tension specimens were simulated in a multi-scale manner and verified experimentally.

Stress Relief in Contact-Aided Compliant Cellular Mechanisms

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Vipul Mehta ◽  
Mary Frecker ◽  
George A. Lesieutre
Keyword(s):  
Finite Element ◽  
Analytical Model ◽  
Stress Relief ◽  
Cellular Structures ◽  
Cellular Mechanisms ◽  
Element Analysis ◽  
Bending Stresses ◽  
Order Of Magnitude ◽  
Structural Mass ◽  
Contact Mechanism

Compliant cellular structures with an internal contact mechanism are described in this paper. Contact during deformation reduces failure-causing bending stresses through stress relief, thereby enabling such cellular structures to be stretched more than the corresponding structures without contact. Finite element analysis (FEA) is carried out to simulate the structure. An analytical model is developed to get results quicker than FEA and to develop insight into the mechanics of the deformation process. The error in prediction of the maximum stretching capacity using the analytical model is less than 7% when compared with finite element simulations. Several materials are investigated for such structures. Although the allowable strain of all these materials is small, the overall strain of the contact-aided cellular structures is at least an order of magnitude greater than that of the constitutive material. The contact mechanism and the induced stress relief increase the stretching capacity of the contact-aided cellular structures by as much as 100%. Experiments are conducted to validate the models, and good agreement is found. A high-strain morphing aircraft skin is examined as an application of these mechanisms. The results indicate that the proposed skin structure not only increases the morphing capacity but also decreases the structural mass by 13% as compared with a cellular skin without contact.

Local Redesign for Additive Manufacturability of Compliant Mechanisms Using Topology Optimization

2021 ◽  
Author(s):  
Stijn Koppen ◽  
Emma Hoes ◽  
Matthijs Langelaar ◽  
Mary I. Frecker
Keyword(s):  
Topology Optimization ◽  
Additive Manufacturing ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Computational Effort ◽  
Manufacturing Constraints ◽  
Design For Additive Manufacturing ◽  
Computationally Efficient ◽  
Stress Levels ◽  
Overhang Angle

Abstract Compliant mechanisms are crucial components in current and future high-precision applications. Topology optimization and additive manufacturing offer freedom to design complex compliant mechanisms that were impossible to realize using conventional manufacturing. Design for additive manufacturing constraints, such as the maximum overhang angle and minimum feature size, tend to drastically decrease the performance of topology optimized compliant mechanisms. It is observed that, among others, design for additive manufacturing constraints are only dominant in the flexure regions. Flexures are most sensitive to manufacturing errors, experience the highest stress levels and removal of support material carries the highest risk of failure. It is crucial to impose these constraints on the flexure regions, while in others part of the compliant mechanism design, these constraints can be relaxed. We propose to first design the global compliant mechanism layout in the full domain without imposing any design for additive manufacturing constraints. Subsequently we redesign selected refined local redesign domains with design for additive manufacturing constraints, whilst simultaneously considering the mechanism performance. The method is applied to a single-input-multi-output compliant mechanism case study, limiting the maximum overhang angle, introducing manufacturing robustness and limiting the maximum stress levels of a selected refined redesign domain. The high resolution local redesigns are detailed and accurate, without a large additional computational effort or decrease in mechanism performance. Thereto, the method proves widely applicable, computationally efficient and effective in its purpose.

Topology Synthesis of Compliant Mechanisms for Nonlinear Force-Deflection and Curved Path Specifications

1999 ◽  
Vol 123 (1) ◽  
pp. 33-42 ◽  
Author(s):  
A. Saxena ◽  
G. K. Ananthasuresh
Keyword(s):  
Finite Element ◽  
Linear Models ◽  
Compliant Mechanisms ◽  
Synthesis Method ◽  
Design Sensitivity ◽  
Finite Element Models ◽  
Geometrically Nonlinear ◽  
Linear Elastic ◽  
Nonlinear Design ◽  
Nonlinear Force

Optimal design methods that use continuum mechanics models are capable of generating suitable topology, shape, and dimensions of compliant mechanisms for desired specifications. Synthesis procedures that use linear elastic finite element models are not quantitatively accurate for large displacement situations. Also, design specifications involving nonlinear force-deflection characteristics and generation of a curved path for the output port cannot be realized with linear models. In this paper, the synthesis of compliant mechanisms is performed using geometrically nonlinear finite element models that appropriately account for large displacements. Frame elements are chosen because of ease of implementation of the general approach and their ability to capture bending deformations. A method for nonlinear design sensitivity analysis is described. Examples are included to illustrate the usefulness of the synthesis method.

Bistable Compliant Four-Bar Mechanisms With a Single Torsional Spring

2006 ◽  
Author(s):  
Adarsh Mavanthoor ◽  
Ashok Midha
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Mechanism Design ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Stored Energy ◽  
Element Analysis ◽  
Bistable Behavior ◽  
Torsional Spring ◽  
Bistable Mechanism

Significant reduction in cost and time of bistable mechanism design can be achieved by understanding their bistable behavior. This paper presents bistable compliant mechanisms whose pseudo-rigid-body models (PRBM) are four-bar mechanisms with a torsional spring. Stable and unstable equilibrium positions are calculated for such four-bar mechanisms, defining their bistable behavior for all possible permutations of torsional spring locations. Finite Element Analysis (FEA) and simulation is used to illustrate the bistable behavior of a compliant mechanism with a straight compliant member, using stored energy plots. These results, along with the four-bar and the compliant mechanism information, can then be used to design a bistable compliant mechanism to meet specified requirements.

Design of a Generic Zero Stiffness Compliant Joint

2010 ◽  
Author(s):  
Femke M. Morsch ◽  
Just L. Herder
Keyword(s):  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Great Promise ◽  
Optimized Design ◽  
Analytic Model ◽  
Total Potential ◽  
Fea Model ◽  
Compliant Joint ◽  
Joint Element ◽  
Cross Axis

The objective of this paper is to design a generic zero stiffness compliant joint. This compliant joint could be used as a generic construction element in a compliant mechanism. To avoid the spring-back behavior of conventional compliant joints, the principle of static balancing is applied, implying that for each position of the joint the total potential energy should be constant. To this end, a conventional balanced mechanism, consisting of two pivoted bodies which are balanced with two zero-free-length springs, is taken as an initial concept. The joint is replaced by a compliant cross-axis flexural pivot and each spring is replaced by a pair of compliant leaf springs. For both parts an analytic model was implemented and a configuration with the lowest energy fluctuation was found through optimization. A FEA model was used to verify the analytic model of the optimized design. A prototype was manufactured and tested. Both the FEA model and the experiment confirm the reduction of the needed moment to rotate the compliant joint. The experiment shows the balanced compliant joint is not completely balanced but the moment required to rotate the joint is reduced by 70%. Thus, a statically balanced compliant generic joint element was designed which bears great promise in designing statically balanced compliant mechanisms and making this accessible to any designer.

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