Reduction of Stress in Plastic Compliant Mechanisms by Introducing Metallic Reinforcement

2017 ◽  
Author(s):  
Joshua Crews ◽  
Ashok Midha ◽  
Lokeswarappa R. Dharani
Keyword(s):  
Stress Relaxation ◽  
Compliant Mechanisms ◽  
Experimental Testing ◽  
Testing Device ◽  
Bending Stress ◽  
New Class ◽  
Metallic Reinforcement ◽  
Creep And Stress Relaxation

A method is provided and validated for redesigning compliant segments to improve their fatigue, creep, and stress relaxation performance. The method reduces the bending stress in the polymer portion of the compliant segment without the need for overall mechanism redesign, by introducing metallic reinforcement and by matching the force-deflection response of the redesigned segment to that of the baseline segment. An example redesign case study is presented and validated with experimental testing using a unique deflection testing device designed for fixed-free compliant mechanisms. This vein of research is undertaken using metallic reinforcement (inserts) toward the development of a new class of compliant mechanisms with significantly greater performance, particularly insofar as the problems of fatigue and creep are concerned.

Creep and Stress Relaxation Behavior of Homogeneous and Reinforced Compliant Mechanisms and Segments

2018 ◽  
Author(s):  
Joshua Crews ◽  
Lokeswarappa R. Dharani ◽  
Ashok Midha
Keyword(s):  
Stress Relaxation ◽  
Compliant Mechanisms ◽  
Test Results ◽  
Stress Relaxation Behavior ◽  
Relaxation Resistance ◽  
New Class ◽  
Engineering Plastics ◽  
Physical Tests ◽  
Metallic Reinforcement ◽  
Creep And Stress Relaxation

Two critical disadvantages of compliant mechanisms constructed of engineering plastics are poor creep and stress relaxation resistance. Metallic reinforcement is investigated as a method to improve the creep and stress relaxation behaviors of compliant mechanisms and compliant segments. The stress relaxation and creep behaviors of homogeneous compliant segments are compared to those of metallic reinforced compliant segments. Special specimens and fixtures were designed for conducting physical tests. Test results show that metallic reinforced compliant segments significantly outperform homogeneous compliant segments with respect to both creep and stress relaxation. This vein of research is undertaken using metallic reinforcement (inserts) toward the development of a new class of compliant mechanisms with significantly greater performance, particularly insofar as the problems of fatigue and creep are concerned.

Fatigue and Failure Behavior of Homogeneous and Reinforced Compliant Mechanism Segments

2018 ◽  
Author(s):  
Joshua Crews ◽  
Lokeswarappa R. Dharani ◽  
Ashok Midha
Keyword(s):  
Compliant Mechanisms ◽  
Fatigue Testing ◽  
Compliant Mechanism ◽  
Qualitative Assessment ◽  
Failure Behavior ◽  
Test Results ◽  
New Class ◽  
Metallic Reinforcement ◽  
Baseline Test ◽  
Comprehensive Study

This paper presents a comprehensive study of the fatigue and failure behavior of both homogeneous and metallic-reinforced compliant segments. Baseline test results are presented for a homogeneous, fixed-free compliant segment constructed of thermoset urethane. The advantages of both polymeric and metallic materials for compliant mechanism construction are leveraged by designing and testing compliant test specimens containing a polymer casing and a metallic reinforcing element. Results obtained from fatigue testing of fixed-free compliant segments in a cyclic loading configuration show that the metallic-reinforced compliant specimens offer superior fatigue performance when compared to the homogeneous baseline specimens. Fractography, both macroscopic and microscopic, is used for a qualitative assessment of the failure behavior. This vein of research is undertaken using metallic reinforcement (inserts) toward the development of a new class of compliant mechanisms with significantly greater performance, particularly insofar as the problems of fatigue and creep are concerned.

scholarly journals Fully-compliant statically-balanced mechanisms without prestressing assembly: concepts and case studies

2011 ◽  
Vol 2 (2) ◽  
pp. 169-174 ◽  
Author(s):  
G. Chen ◽  
S. Zhang
Keyword(s):  
Stress Relaxation ◽  
Force Feedback ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
High Fidelity ◽  
Constant Force ◽  
Force Transmission ◽  
Actuation Force ◽  
New Concepts ◽  
Creep And Stress Relaxation

Abstract. The purpose of this paper is to present new concepts for designing fully-compliant statically-balanced mechanisms without prestressing assembly. A statically-balanced compliant mechanism can ideally provide zero stiffness and energy free motion like a traditional rigid-body mechanism. These characteristics are important in design of compliant mechanisms where low actuation force, accurate force transmission or high-fidelity force feedback are primary concerns. Typically, static balancing of compliant mechanisms has been achieved by means of prestressing assembly. However, this can often lead to creep and stress relaxation arising in the flexible members. In this paper two concepts are presented which eliminate the need for prestressing assembly of compliant mechanisms: (1) a weight compensator which employs a constant-force compliant mechanism, (2) a near-zero-stiffness mechanism which combines two multistable mechanisms. In addition to the advantages provided by statically-balanced compliant mechanisms, two other notable features of these statically-balanced mechanisms are their ability to be monolithically fabricated and to return to their as-fabricated position without any disassembly when not in use.

Unsteady creep and stress relaxation of AK4-1 alloy in the probability aspect

1975 ◽  
Vol 7 (1) ◽  
pp. 27-31
Author(s):  
S. P. Borisov ◽  
N. I. Borshchev ◽  
M. N. Stepnov ◽  
I. I. Khazanov
Keyword(s):  
Stress Relaxation ◽  
Unsteady Creep ◽  
Creep And Stress Relaxation

Use of DNVGL-RP-C203 for Determining the Fatigue Capacity of Connectors

2021 ◽  
Author(s):  
Anthony Muff ◽  
Anders Wormsen ◽  
Torfinn Hørte ◽  
Arne Fjeldstad ◽  
Per Osen ◽  
...  
Keyword(s):  
Finite Element ◽  
Fatigue Testing ◽  
Experimental Testing ◽  
High Strength ◽  
Element Model ◽  
Fatigue Analysis ◽  
Full Scale ◽  
The Finite Element Model

Abstract Guidance for determining a S-N based fatigue capacity (safe life design) for preloaded connectors is included in Section 5.4 of the 2019 edition of DNVGL-RP-C203 (C203-2019). This section includes guidance on the finite element model representation, finite element based fatigue analysis and determination of the connector design fatigue capacity by use of one of the following methods: Method 1 by FEA based fatigue analysis, Method 2 by FEA based fatigue analysis and experimental testing and Method 3 by full-scale connector fatigue testing. The FEA based fatigue analysis makes use of Appendix D.2 in C203-2019 (“S-N curves for high strength steel applications for subsea”). Practical use of Section 5.4 is illustrated with a case study of a fatigue tested wellhead profile connector segment test. Further developments of Section 5.4 of C203-2019 are proposed. This included acceptance criteria for use of a segment test to validate the FEA based fatigue analysis of a full-scale preloaded connector.

A Case Study - NeuBase Therapeutics, Inc.

2021 ◽  
Vol 26 (2) ◽  
Author(s):  
Dietrich A. Stephan
Keyword(s):  
Gene Function ◽  
Genetic Defects ◽  
New Class ◽  
Genetic Revolution

NeuBase is accelerating the genetic revolution by developing a new class of precision genetic medicines which can be designed to increase, decrease, or change gene function, as appropriate, to resolve genetic defects that drive disease.

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