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Design Innovation Paper

Design of a Portable Compliant Device for Estimating the Failure-Load of Mesoscale Cemented Sand Specimens

[+] Author and Article Information
Santosh D. B. Bhargav

Department of Mechanical Engineering,
Indian Institute of Science,
Bangalore Karnataka, India
e-mail: sbhargav@mecheng.iisc.ernet.in

Ramesh K. Kandasami

Department of Civil Engineering,
Indian Institute of Science,
Bangalore Karnataka, India
e-mail: rameshkk@civil.iisc.ernet.in

Tejas G. Murthy

Department of Civil Engineering,
Indian Institute of Science,
Bangalore Karnataka, India
e-mail: tejas@civil.iisc.ernet.in

G. K. Ananthasuresh

Department of Mechanical Engineering,
Indian Institute of Science,
Bangalore Karnataka, India
e-mail: suresh@mecheng.iisc.ernet.in

Contributed by the Design Innovation and Devices of ASME for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received July 21, 2014; final manuscript received February 19, 2015; published online March 18, 2015. Assoc. Editor: Shorya Awtar.

J. Mech. Des 137(6), 065001 (Jun 01, 2015) (8 pages) Paper No: MD-14-1432; doi: 10.1115/1.4029893 History: Received July 21, 2014; Revised February 19, 2015; Online March 18, 2015

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 100 N 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 10 mm in diameter and 20 mm 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 0.95 N 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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Figures

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Fig. 1

(a) Symmetric-half of a compliant gripper. (b) SL model of a compliant gripper without the external effects. (c) SL model with external effects such as actuator stiffness and external specimen stiffness. (d) A sample of 3D feasible volume in the 3D space of kci-kco-n.

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Fig. 7

(a) A typical graph that is obtained while manipulating a cemented sand specimen. (b) A typical force versus displacement plot obtained while estimating the failure-load. The compliant tool is compared with the DMA.

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Fig. 2

(a) Feasible region is drawn based on the user specifications. It also shows the location of the existing mechanisms on the plot. (b) Deformed and undeformed configuration of the chosen mechanism. (c) Depending on the size of the specimen the mechanism applies the load on the specimen with different value of mechanical advantage.

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Fig. 3

SL model of the composite compliant mechanism developed for testing cemented sand specimen

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Fig. 4

Feasible region is drawn based on the user specifications. It also shows the location of the existing mechanisms on the plot.

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Fig. 5

(a) Final design of the composite mechanism. (b) The deformed and undeformed configuration of the final design.

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Fig. 6

(a) Fabricated composite mechanism. (b) The points on the mechanism where the displacements are estimated. (c) Curve obtained to relate the displacements at the amplified point of the mechanism and the point that is in contact with the specimen. (d) Experimentally obtained curve comparing the voltage sensed by the Hall effect sensor and the distance between the former and the magnet.

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