Design of a Portable Compliant Device for Estimating the Failure-Load of Mesoscale Cemented Sand Specimens
01 Jun 2015-Journal of Mechanical Design (American Society of Mechanical Engineers)-Vol. 137, Iss: 6, pp 065001
TL;DR: In this paper, a hand-operated compliant mechanism for estimating the failure load of cm-sized stiff objects whose stiffness is of the order of 10 s of kN/m was presented.
Abstract: In this paper, we present the design and development of a portable, hand-operated composite compliant mechanism for estimating the failure-load of cm-sized stiff objects whose stiffness is of the order of 10 s of kN/m. The motivation for the design comes from the need to estimate the failure-load of mesoscale cemented sand specimens in situ, which is not possible with traditional devices used for large specimens or very small specimens. The composite compliant device, developed in this work, consists of two compliant mechanisms: a force-amplifying compliant mechanism (FaCM) to amplify sufficiently the force exerted by hand in order to break the specimen and a displacement-amplifying compliant mechanism (DaCM) to enable measurement of the force using a proximity sensor. The two mechanisms are designed using the selection-maps technique to amplify the force up to 100N by about a factor of 3 and measure the force with a resolution of 15 mN. The composite device, made using a FaCM, a DaCM, and a Hall effect-based proximity sensor, was tested on mesoscale cemented sand specimens that were 10mm in diameter and 20mm in length. The results are compared with those of a large commercial instrument. Through the experiments, it was observed that the failure-load of the cemented sand specimens varied from 0.95N to 24.33 N, depending on the percentage of cementation and curing period. The estimation of the failure-load using the compliant device was found to be within 1.7% of the measurements obtained using the commercial instrument and thus validating the design. The details of the design, prototyping, specimen preparation, testing, and the results comprise the paper.
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TL;DR: This paper focuses on optimizing the skeletal shape of the compliant segments in a given topology by identifying such segments in the topology and representing them using Bezier curves, and presents analytical sensitivity analysis for the objective and constraints.
Abstract: Compliant mechanisms are elastic continua used to transmit or transform force and motion mechanically. The topology optimization methods developed for compliant mechanisms
also give the shape for a chosen parameterization of the design domain with a fixed mesh. However, in these methods, the shapes of the flexible segments in the resulting
optimal solutions are restricted either by the type or the resolution of the design parameterization. This limitation is overcome in this paper by focusing on optimizing the skeletal shape of the compliant segments in a given topology. It is accomplished by identifying
such segments in the topology and representing them using Bezier curves. The vertices of the Bezier control polygon are used to parameterize the shape-design space. Uniform
parameter steps of the Bezier curves naturally enable adaptive finite element discretization of the segments as their shapes change. Practical constraints such as avoiding
intersections with other segments, self-intersections, and restrictions on the available space and material, are incorporated into the formulation. A multi-criteria function from our prior work is used as the objective. Analytical sensitivity analysis for the objective
and constraints is presented and is used in the numerical optimization. Examples are included to illustrate the shape optimization method.
87 citations
"Design of a Portable Compliant Devi..." refers methods in this paper
...This is a FaCM reported by Xu and Ananthasuresh [18]....
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...Shape optimization methods are also used to improve the performance further by optimizing the shape [18,19]....
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TL;DR: A vision-based force-sensing technique by solving Cauchy's problem in elasticity using an improved algorithm is presented and validated at the macroscale, where there was an independent method to estimate the force.
Abstract: This paper is concerned with grasping biological cells in aqueous medium with miniature grippers that can also help estimate forces using vision-based displacement measurement and computation. We present the design, fabrication, and testing of three single-piece, compliant miniature grippers with parallel and angular jaw motions. Two grippers were designed using experience and intuition, while the third one was designed using topology optimization with implicit manufacturing constraints. These grippers were fabricated using different manufacturing techniques using spring steel and polydimethylsiloxane (PDMS). The grippers also serve the purpose of a force sensor. Toward this, we present a vision-based force-sensing technique by solving Cauchy's problem in elasticity using an improved algorithm. We validated this technique at the macroscale, where there was an independent method to estimate the force. In this study, the gripper was used to hold a yeast ball and a zebrafish egg cell of less than 1 mm in diameter. The forces involved were estimated to be about 30 and 10 mN for the yeast ball and the zebrafish egg cell, respectively.
73 citations
"Design of a Portable Compliant Devi..." refers methods in this paper
...simultaneously actuating a specimen while also sensing the force using measured displacements and solving an inverse problem to compute the forces [14]....
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TL;DR: In this paper, the authors present the results of a numerical study carried out by 2D discrete element method analyses on the mechanical behavior and strain localization of loose cemented granular materials.
Abstract: This paper presents the results of a numerical study carried out by 2D discrete element method analyses on the mechanical behavior and strain localization of loose cemented granular materials. Bonds between particles were modeled in order to replicate the mechanical behavior observed in a series of laboratory tests performed on pairs of glued aluminum rods which can fail either in tension or shear (Jiang et al. in Mech Mater 55:1–15, 2012). This bond model was implemented in a DEM code and a series of biaxial compression tests employing lateral flexible boundaries were performed. The influence of bond strength and confinement levels on the mechanical behavior and on the onset of shear bands and their propagation within the specimens were investigated. Comparisons were also drawn with other bond models from the literature. A new dimensionless parameter incorporating the effects of both bond strength and confining pressure, called BS, was defined. The simulations show that shear strength and also dilation increase with the level of bond strength. It was found out that for increasing bond strength, shear bands become thinner and oriented along directions with a higher angle over the horizontal. It also emerged that the onset of localization coincided with the occurrence of bond breakages concentrated in some zones of the specimens. The occurrence of strain localization was associated with a concentration of bonds failing in tension.
65 citations
"Design of a Portable Compliant Devi..." refers background in this paper
...Simulations of interparticle interactions and their extrapolation to a macroscale response of granular materials have provided extraordinary insight into the mechanics of the cemented sands [6,7]....
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TL;DR: In this article, a shape and size synthesis method for compliant mechanisms based on free-form wide curve theory is proposed, in which every connection in the topology is represented by a parametric wide curve.
Abstract: A wide curve is a curve with width or cross section. This paper introduces a shape and size synthesis method for compliant mechanisms based on free-form wide curve theory. With the proposed method, detailed dimensions synthesis can be performed to further improve the performance after the topology is selected. Every connection in the topology is represented by a parametric wide curve in which variable shape and size are fully described and conveniently controlled by the limited number of parameters. The shape and size synthesis is formulated as the optimization of the control parameters of wide curves corresponding to all connections in the topology. Problem-dependent objectives are optimized and practical constraints are imposed during the optimization process. The optimization problem is solved by the constrained nonlinear programing algorithm in the MATLAB Optimization Toolbox. Two examples are included to demonstrate the effectiveness of the proposed synthesis procedure.
57 citations
"Design of a Portable Compliant Devi..." refers methods in this paper
...Shape optimization methods are also used to improve the performance further by optimizing the shape [18,19]....
[...]
01 Jan 1999
TL;DR: In this article, the authors describe design, microfabrication and characterisation of topology optimised compliant electro-thermal microactuators, which are fabricated by a fast prototyping process using laser micromachining and electroplating.
Abstract: This paper describes design, microfabrication and characterisation of topology optimised compliant electro-thermal microactuators. The actuators are fabricated by a fast prototyping process using laser micromachining and electroplating. Actuators are characterised with respect to displacement, force and work, by use of image analysis. Four different actuators are presented. These actuators are capable of displacements of 30 /spl mu/m and forces of 15 mN. The most recent actuator designs function in reasonable accordance with design predictions.
54 citations
Additional excerpts
...They can be used as transmissions [10], actuators [11], and sensors [12,13]....
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