The Accurate Modeling and Performance Analysis of Cross-Spring Pivot as a Flexure Module

2008 ◽  
Author(s):  
Hongzhe Zhao ◽  
Shusheng Bi ◽  
Jingjun Yu ◽  
Guanghua Zong
Keyword(s):  
Compliant Mechanisms ◽  
Bending Moment ◽  
Element Analysis ◽  
Rotational Angle ◽  
Rotational Displacement ◽  
Center Shift ◽  
Rotational Element ◽  
Displacement Behavior ◽  
And Performance ◽  
Relative Errors

The load-displacement behavior of a cross-spring pivot as a kind of rotational element or module in compliant mechanisms is a subject of keen interest for many researchers. The model allowing not only quick design but also characteristics capture is pursued. This paper addresses some accurate closed-form results via approximations. These expressions are simple for a designer to understand the parameters without resorting to a tedious iterative procedure. The rotational displacement and center shift of the pivot are analyzed both qualitatively and quantitatively, with a general-purposed load applied including bending moment, horizontal and vertical forces. Meanwhile, a concise expression for center shift without approximations is proposed. The validity of the model is verified by finite element analysis (FEA). The relative error of the rotational displacement is less than 1.8% even if the rotational angle reaches ±20° the relative errors for the two components of center shift are less than 6% and 4% respectively, in the case of typical but general configurations and loads.

Modeling of a Cartwheel Flexural Pivot

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
Bi Shusheng ◽  
Zhao Hongzhe ◽  
Yu Jingjun
Keyword(s):  
Parametric Design ◽  
Bending Moment ◽  
Equivalent Model ◽  
Vertical Force ◽  
Element Analysis ◽  
Rotational Angle ◽  
Single Beam ◽  
Primary Motion ◽  
Center Shift ◽  
Parasitic Motion

A cartwheel flexural pivot has a small center shift as a function of loading and ease of manufacturing. This paper addresses an accurate model that includes the loading cases of a bending moment combined with both a horizontal force and a vertical force. First, a triangle flexural pivot is modeled as a single beam. Then, the model of cartwheel flexural pivot based on an equivalent model is developed by utilizing the results of the triangle pivot. The expressions for rotational displacement and center shift are derived to evaluate the primary motion and the parasitic motion; the maximum rotational angle is simply formulated to predicate the range of motion. Finally, the model is verified by finite element analysis. The relative error of the primary motion is less than 1.1% for various loading cases even if the rotational angle reaches ±20 deg, and the predicted errors for the two center shift components are less than 15.4% and 7.1%. The result shows that the model is accurate enough for designers to use for initial parametric design studies, such as for conceptual design.

Analytical Modeling and Analysis of an Annulus-Shaped Flexural Pivot

2012 ◽  
Author(s):  
Yanbin Yao ◽  
Shusheng Bi ◽  
Hongzhe Zhao
Keyword(s):  
Analytical Modeling ◽  
Compliant Mechanisms ◽  
Bending Moment ◽  
Vertical Force ◽  
Rotational Stiffness ◽  
Element Analysis ◽  
Rotational Angle ◽  
Modeling And Analysis ◽  
The Finite Element Analysis ◽  
Constraint Model

Annulus-shaped flexural pivots (ASFP), composed of three or more identical leaves that are symmetrically arrayed in an annulus, can be used widely in compliant mechanisms for their excellent performances. This paper proposes the accurate load-rotation models of ASFP with three straight leaves, which include the load cases of bending moment combined with horizontal force and vertical force. Firstly, the load-rotation models of ASFP are derived based on the Beam Constraint Model (BCM). Then, the rotational stiffness and buckling characteristics are analyzed based on the derived models. Finally, the accuracy of the models is validated by the finite element analysis (FEA). The relative error of the load-rotation models is within 7% for various load cases even if the rotational angle reaches 0.07 (4°). The results show that the models are accurate enough to be used for initial parametric designing of ASFP.

scholarly journals Shear Performance of Optimized-Section Precast Slab with Tapered Cross Section

2018 ◽  
Vol 11 (1) ◽  
pp. 163 ◽  
Author(s):  
Hyunjin Ju ◽  
Sun-Jin Han ◽  
Hyo-Eun Joo ◽  
Hae-Chang Cho ◽  
Kang Kim ◽  
...  
Keyword(s):  
Cross Section ◽  
Design Method ◽  
Precast Concrete ◽  
Bending Moment ◽  
Shear Behaviour ◽  
Element Analysis ◽  
Cross Sectional ◽  
Shear Design ◽  
Shear Performance ◽  
And Performance

The optimized-section precast slab (OPS) is a half precast concrete (PC) slab that highlights structural aesthetics while reducing the quantity of materials by means of an efficient cross-sectional configuration considering the distribution of a bending moment. However, since a tapered cross section where the locations of the top and bottom flanges change is formed at the end of the member, stress concentration occurs near the tapered cross section because of the shear force and thus the surrounding region of the tapered cross section may become unintentionally vulnerable. Therefore, in this study, experimental and numerical research was carried out to examine the shear behaviour characteristics and performance of the OPS with a tapered cross section. Shear tests were conducted on a total of eight OPS specimens, with the inclination angle of the tapered cross section, the presence of topping concrete and the amount of shear reinforcement as the main test variables and a reasonable shear-design method for the OPS members was proposed by means of a detailed analysis based on design code and finite-element analysis.

Design and Modeling of a Variable Thickness Flexure Pivot

2018 ◽  
Vol 11 (1) ◽  
Author(s):  
Miao Yang ◽  
Zhijiang Du ◽  
Wei Dong ◽  
Lining Sun
Keyword(s):  
Axial Force ◽  
Variable Thickness ◽  
Compliant Mechanisms ◽  
Experimental Tests ◽  
Deformation Model ◽  
Element Analysis ◽  
Center Shift ◽  
Motion Range ◽  
Rotation Stiffness ◽  
Long Stroke

Flexure pivots are frequently applied in long stroke compliant mechanisms to transmit motion continuously. To improve the motion accuracy, a kind of variable thickness flexure pivot (VTFP) is proposed in this paper. A nonlinear beam element is proposed by utilizing the corotational approach to model the static response of the VTFP under end loads. Finite element analysis and experimental tests are carried out to verify the effectiveness of the modeling method. Based on the static deformation model, the motion range, the rotation stiffness, the center shift, and the variation of the center shift under axial force of the VTFP are investigated. The results show that the VTFP has better motion accuracy and better ability to resist axial force compared with the conventional flexure pivot.

Deterministic Design for a Compliant Parallel Universal Joint With Constant Rotational Stiffness

2018 ◽  
Vol 10 (3) ◽  
Author(s):  
Yan Xie ◽  
Jingjun Yu ◽  
Hongzhe Zhao
Keyword(s):  
Compliant Mechanisms ◽  
Experimental Testing ◽  
Rotational Stiffness ◽  
Universal Joint ◽  
Element Analysis ◽  
Rotational Angle ◽  
Constant Stiffness ◽  
Stiffness Model ◽  
Stiffness Characteristics ◽  
Constraint Model

Compliant universal joints have been widely employed in high-precision fields due to plenty of good performance. However, the stiffness characteristics, as the most important consideration for compliant mechanisms, are rarely involved. In this paper, a deterministic design for a constraint-based compliant parallel universal joint with constant rotational stiffness is presented. First, a constant stiffness realization principle is proposed by combination of the freedom and constraint topology (FACT) method and beam constraint model (BCM) to establish a mapping relationship between stiffness characteristics and topology configurations. A parallel universal joint topology is generated by the constant stiffness realization principle. Then, the analytical stiffness model of the universal joint with some permissible approximations is formulated based on the BCM, and geometrical prerequisites are derived to achieve the desired constant rotational stiffness. After that, finite element analysis (FEA), experimental testing, and detailed stiffness analysis are carried out. It turns out that the rotational stiffness of the universal joint can keep constant with arbitrary azimuth angles even if the rotational angle reaches up to ±5 deg. Meanwhile, the acceptable relative errors of rotational stiffness are within 0.53% compared with the FEA results and 2.6% compared with the experimental results, which indicates the accuracy of the theoretical stiffness model and further implies the feasibility of constant stiffness realization principle on guiding the universal joint design.

Character Analysis of Balance and Imbalance of Varying Rigidity of Rigid Pile Composite Foundation under Seismic Load

2014 ◽  
Vol 1065-1069 ◽  
pp. 19-22
Author(s):  
Zhen Feng Wang ◽  
Ke Sheng Ma
Keyword(s):  
Finite Element ◽  
Bending Moment ◽  
Horizontal Displacement ◽  
Element Model ◽  
Composite Foundation ◽  
Seismic Load ◽  
Seismic Loads ◽  
Element Analysis ◽  
Rigid Pile ◽  
Rigid Pile Composite Foundation

Based on ABAQUS finite element analysis software simulation, the finite element model for dynamic analysis of rigid pile composite foundation and superstructure interaction system is established, which selects the two kinds of models, by simulating the soil dynamic constitutive model, selecting appropriate artificial boundary.The influence of rigid pile composite foundation on balance and imbalance of varying rigidity is analyzed under seismic loads. The result shows that the maximum bending moment and the horizontal displacement of the long pile is much greater than that of the short pile under seismic loads, the long pile of bending moment is larger in the position of stiffness change. By constrast, under the same economic condition, the aseismic performance of of rigid pile composite foundation on balance of varying rigidity is better than that of rigid pile composite foundation on imbalance of varying rigidity.

Tensegrity Structures in the Design of Flexible Structures for Offshore Aquaculture

2007 ◽  
Author(s):  
O̸sten Jensen ◽  
Anders Sunde Wroldsen ◽  
Pa˚l Furset Lader ◽  
Arne Fredheim ◽  
Mats Heide ◽  
...  
Keyword(s):  
Flexible Structures ◽  
Weather Conditions ◽  
High Energy ◽  
Open Ocean ◽  
Element Analysis ◽  
Tensegrity Structures ◽  
Stiffness Properties ◽  
Offshore Aquaculture ◽  
And Performance ◽  
Open Ocean Aquaculture

Aquaculture is the fastest growing food producing sector in the world. Considerable interest exists in developing open ocean aquaculture in response to a shortage of suitable, sheltered inshore locations. The harsh weather conditions experienced offshore lead to a focus on new structure concepts, remote monitoring and a higher degree of automation in order to keep the cost of structures and operations within an economically viable range. This paper proposes tensegrity structures in the design of flexible structures for offshore aquaculture. The finite element analysis program ABAQUS™ has been used to investigate stiffness properties and performance of tensegrity structures when subjected to various forced deformations and hydrodynamic load conditions. The suggested concept, the tensegrity beam, shows promising stiffness properties in tension, compression and bending, which are relevant for development of open ocean aquaculture construction for high energy environments. When designing a tensegrity beam, both pre-stress and spring stiffness should be considered to ensure the desired structural properties. A large strength to mass ratio and promising properties with respect to control of geometry, stiffness and vibration could make tensegrity an enabling technology for future developments.

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.

Preliminary Parametric Assessment of a Bolted Endplate Joint under Combined Axial Force and Cyclic Bending Moment

2011 ◽  
Vol 255-260 ◽  
pp. 718-721
Author(s):  
Z.Y. Wang ◽  
Q.Y. Wang
Keyword(s):  
Finite Element Analysis ◽  
Axial Force ◽  
Seismic Design ◽  
Axial Load ◽  
Failure Modes ◽  
Bending Moment ◽  
Element Analysis ◽  
Cyclic Behaviour ◽  
Joint Behaviour ◽  
Steel Joints

Problems regarding the combined axial force and bending moment for the behaviour of semi-rigid steel joints under service loading have been recognized in recent studies. As an extended research on the cyclic behaviour of a bolted endplate joint, this study is performed relating to the contribution of column axial force on the cyclic behaviour of the joint. Using finite element analysis, the deteriorations of the joint performance have been evaluated. The preliminary parametric study of the joint is conducted with the consideration of flexibility of the column flange. The column axial force was observed to significantly influence the joint behaviour when the bending of the column flange dominates the failure modes. The reductions of moment resistance predicted by numerical analysis have been compared with codified suggestions. Comments have been made for further consideration of the influence of column axial load in seismic design of bolted endplate joints.

ANALYSIS OF AN INTERNAL FIXATION OF A LONG BONE FRACTURE

2005 ◽  
Vol 05 (01) ◽  
pp. 89-103 ◽  
Author(s):  
K. RAMAKRISHNA ◽  
I. SRIDHAR ◽  
S. SIVASHANKER ◽  
V. K. GANESH ◽  
D. N. GHISTA
Keyword(s):  
Stress Shielding ◽  
Axial Loading ◽  
Bending Moment ◽  
Fracture Site ◽  
Long Bone ◽  
Radius Of Curvature ◽  
Element Analysis ◽  
Long Bone Fracture ◽  
Fracture Interface ◽  
Tensile Surface

A major concern when a fractured bone is fastened by stiff-plates to the bone on its tensile surface is excessive stress shielding of the bone. The compressive stress shielding at the fracture-interface immediately after fracture-fixation delays bone healing. Likewise, the tensile stress shielding of the healed bone underneath the plate also does not enable it to recover its tensile strength. Initially, the effect of a uniaxial load and a bending moment on the assembly of bone and plate is investigated analytically. The calculations showed that the screws near the fracture site transfers more load than the screws away from the fracture site in axial loading and it is found that less force is required when the screw is placed near to fracture site than the screw placed away from the fracture site to make the bone and plate bend with same radius of curvature when subjected to bending moment. Finally, the viability of using a stiffness graded bone-plate as a fixator is studied using finite element analysis (FEA): the stiffness-graded plate cause less stress-shielding than stainless steel plate.

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