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

Abstract

In this paper, we present the design and development of a portable, handoperated composite compliant mechanism for estimating the failureload of cmsized 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 failureload 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 forceamplifying compliant mechanism (FaCM) to amplify sufficiently the force exerted by hand in order to break the specimen and a displacementamplifying compliant mechanism (DaCM) to enable measurement of the force using a proximity sensor. The two mechanisms are designed using the selectionmaps 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 effectbased 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 failureload 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 failureload 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.