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%.

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.

Contact-aided compliant mechanisms for morphing aircraft skin

2008 ◽  
Author(s):  
Vipul Mehta ◽  
Mary Frecker ◽  
George Lesieutre
Keyword(s):  
Compliant Mechanisms ◽  
Morphing Aircraft ◽  
Aircraft Skin

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%.

Dynamic Behaviors of near β-Type Ti-5Al-5Mo-5V-3Cr Titanium Alloys under High Strain Rate

2015 ◽  
Vol 816 ◽  
pp. 795-803
Author(s):  
Yan Ling Wang ◽  
Song Xiao Hui ◽  
Wen Jun Ye ◽  
Rui Liu
Keyword(s):  
Strain Rate ◽  
Titanium Alloys ◽  
High Strain ◽  
Split Hopkinson Pressure Bar ◽  
Failure Behavior ◽  
Hopkinson Pressure Bar ◽  
Fracture Failure ◽  
Split Hopkinson ◽  
Pressure Bar ◽  
Dynamic Loading Conditions

The mechanical properties and fracture failure behavior of the near β-type Ti-5Al-5Mo-5V-3Cr-X (X = 1Fe or 1Zr) titanium alloys were studied by Split Hopkinson Pressure Bar (SHPB) experiment under the dynamic loading conditions at a strain rate of 1.5 × 103 s-1–5.0 × 103 s-1. Results showed that the SHPB specimen fractured in the direction of maximum shearing stress at an angle of 45° with the compression axis. The fracture surface revealed the shear and tension zones with cleavage steps and parabolic dimples. Severe early unloading was observed on the Ti-5553 alloy under a strain rate of 4,900 s-1 loading condition, and the dynamic property of the Ti-55531Zr alloy was proved to be the optimal.

Design of a Compliant Endoscopic Suturing Instrument

2008 ◽  
Vol 2 (2) ◽  
Author(s):  
James A. Cronin ◽  
Mary I. Frecker ◽  
Abraham Mathew
Keyword(s):  
Finite Element Analysis ◽  
Minimally Invasive Surgery ◽  
Compliant Mechanisms ◽  
Stress Relief ◽  
Natural Orifice ◽  
Endoscopic Suturing ◽  
Element Analysis ◽  
Design And Optimization ◽  
Puncture Force ◽  
Nonlinear Deformations

This paper describes the initial design and optimization of a compliant endoscopic suturing instrument. The emerging field of Natural Orifice Transluminal Endoscopic Surgery (NOTES) requires innovative instruments to meet the size limitations inherent in this type of minimally invasive surgery; using compliant mechanisms is proposed as one method of meeting this requirement. The compliant design was modeled and optimized to maximize the distal opening and provide a puncture force of at least 4.6N, while being small enough to fit within a 3.3mm working channel. The design utilizes contact for stress relief and intertwining parts for added deflection. ANSYS® was used for finite element analysis including contact and nonlinear deformations. A prototype was fabricated from the optimized geometry and experimentally tested. The best geometry is predicted to have a distal opening of 14.6mm at the tips and supply a puncturing force of 4.83N. The force supplied at the tip was measured and was found to exceed the required 4.6N. The prototype successfully passed two complete sutures and qualitative results are provided. The results of the study will lead to further refinements and improvements in future designs.

scholarly journals Thermoplastic Composites for Integrally Woven Pressure Actuated Cellular Structures: Design Approach and Material Investigation

Polymers ◽  
2021 ◽  
Vol 13 (18) ◽  
pp. 3128
Author(s):  
Michael Vorhof ◽  
Cornelia Sennewald ◽  
Philipp Schegner ◽  
Patrick Meyer ◽  
Christian Hühne ◽  
...  
Keyword(s):  
Compliant Mechanisms ◽  
Thermoplastic Composites ◽  
Cellular Structures ◽  
Experimental Investigations ◽  
Deformation Capacity ◽  
High Deformation Rate ◽  
Double Row ◽  
High Deformation ◽  
Textile Preform ◽  
Further Development

The use of pressure-actuated cellular structures (PACS) is an effective approach for the application of compliant mechanisms. Analogous to the model in nature, the Venus flytrap, they are made of discrete pressure-activated rows and can be deformed with high stiffness at a high deformation rate. In previous work, a new innovative approach in their integral textile-based manufacturing has been demonstrated based on the weaving technique. In this work, the theoretical and experimental work on the further development of PACS from simple single-row to double-row PACS with antagonistic deformation capability is presented. Supported by experimental investigations, the necessary adaptations in the design of the textile preform and the polymer composite design are presented and concretized. Based on the results of pre-simulations of the deformation capacity of the new PACS, their performance was evaluated, the results of which are presented.

An Automated Design Synthesis Method for Compliant Mechanisms With Application to Morphing Wings

2006 ◽  
Author(s):  
Hongqing Vincent Wang ◽  
David W. Rosen
Keyword(s):  
Particle Swarm Optimization ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Synthesis Method ◽  
Particle Swarm ◽  
Automated Design ◽  
Cellular Structures ◽  
Swarm Optimization ◽  
Design Synthesis ◽  
Axial Forces

An automated design synthesis method is developed to design an airfoil with a reconfigurable shape, which can change from one type of geometry to another. A design synthesis method using unit truss approach and particle swarm optimization is presented. In the unit truss approach, unit truss is used as a new unit cell for mechanics analysis of cellular structures, including lightweight structures and compliant mechanisms. Using unit truss approach, axial forces, bending, torsion, nonlinearity, and buckling in structures can be considered. It provides good analysis accuracy and computational efficiency. A synthesis method using unit truss approach integrated with particle swarm optimization is developed to systematically design adaptive cellular structures, in particular, compliant mechanisms discussed in this paper. As an example study, the authors realize the design synthesis of a compliant mechanism that enables an entire closed-loop airfoil profile to change shape from NACA 23015 to FX60-126 for the desired morphing wing. The nonlinear behavior of compliant mechanisms under large deformation is considered. The resulting design is validated by testing its robustness and considering nonlinearity.

Design of a Compliant Endoscopic Suturing Instrument

2007 ◽  
Author(s):  
James A. Cronin ◽  
Mary Frecker ◽  
Abraham Mathew
Keyword(s):  
Minimally Invasive Surgery ◽  
Minimally Invasive ◽  
Compliant Mechanisms ◽  
Stress Relief ◽  
Initial Study ◽  
Response Patterns ◽  
Natural Orifice ◽  
Endoscopic Suturing ◽  
Jaw Opening ◽  
Puncture Force

This paper outlines the development and initial optimization of a compliant endoscopic suturing instrument. The developing field of Natural Orifice Transluminal Endoscopic Surgery requires innovative instruments to meet the size limitations inherent in this type of minimally invasive surgery; using compliant mechanisms is proposed as one method of meeting this requirement. Three initial compliant designs were created, modeled, and compared for a distal opening of 10 mm. Restricting these designs so that they must fit within a 3.3 mm working channel is currently unique in endoscopic suturing instruments. A design that utilizes contact for stress relief and intertwining parts for added deflection was selected from the three. ANSYS® was used to aid in graphical optimization to maximize the jaw opening and maximize the puncture force of the selected design. The best geometry has a distal opening of 13.8 mm at the tips and can supply a puncturing force of 6.33 N. A prototype has been machined using the optimized dimensions and is ready to be tested. This initial study in compliant suturing instrument designs has revealed response patterns for the chosen geometries that will lead to further refinements and improvements in future models.

Strain Capacity Investigation on Grade X70 High Strain Line Pipe With Girth Weld

2018 ◽  
Author(s):  
Hisakazu Tajika ◽  
Takahiro Sakimoto ◽  
Tsunehisa Handa ◽  
Satoshi Igi ◽  
Rinsei Ikeda ◽  
...  
Keyword(s):  
High Strain ◽  
Compressive Strain ◽  
Bending Test ◽  
High Grade ◽  
Line Pipe ◽  
Strain Capacity ◽  
Global Strain ◽  
Significant Difference ◽  
Pipeline Project ◽  
Pipe Bending

Recently high grade pipeline project have been planned in hostile environment like landslide in mountain area, liquefaction in reclaimed land or the frost heave in Polar Regions. Geohazards bring large scale ground deformation and effect on the varied pipeline to cause large deformation. Therefore, strain capacity is important for the pipeline and strain based design is also needed to keep gas transportation project in safe. High grade steel pipe for linepipe tends to have higher yield to tensile (Y/T) ratio and it has been investigated that the lower Y/T ratio of the material improves strain capacity in buckling and tensile limit state. In onshore pipeline project, pipe usually transported in 12 or 18m each and jointed in the field. Girth weld (GW) is indispensable so strength matching of girth weld towards pipe body is important. In this study strain capacity of Grade X70 high strain pipe with size of 36” OD and 23mm WT was investigated with two types of experiments. One was a pipe bending test with whole pipe. The length of the specimen was approximately 8m and GW was made in the middle of joint length. A fixed internal pressure was applied during the bending test. Actual pipe situation in work was simulated and both circumferential and longitudinal stress occurred in this test. The other test was curved wide plate (CWP) test. In both tests, test pipes were cut and welded using GTAW in the first two layers and GMAW for the subsequent passes. Welding wire of TG-S62 and MG-S58P were used for GTAW and GMAW respectively to achieve over-matching girth weld considering the pipe body strength. Elliptical EDM notch was installed in the GW HAZ as simulated weld defect. In pipe bending test, buckling occurred at the intrados at 300 mm apart from the GW. 2D average compressive strain at buckling was 3.59% and this high compressive strain was considered to derive from the high strain capacity of this pipes. After the buckling, deformation concentrated to the buckling wrinkle. Test pipe broke at 35.5 degrees of pipe end rotation and the location was in base metal at the extrados opposite to the buckling wrinkle. The HAZ notch opened and CTOD was 1.44 mm and the global strain in 2D length average strain was 7.8%. In CWP test, tensile strain simply got large and pipe finally broke at global strain of 9.6% and CTOD of 15 mm. The break location was the HAZ notch. There was a significant difference in CTOD growth in HAZ between two test types. Conditions and factors that effect to these differences are argued in this paper.

Sign in / Sign up

Export Citation Format

Share Document