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# A Linear Laser Scanner to Measure Cross-Sectional Shape and Area of Biological Specimens During Mechanical Testing

[+] Author and Article Information
Claudio Vergari1

USC INRA-ENVA, Biomécanique et Pathologie Locomotrice du Cheval, Ecole Nationale Vétérinaire d’Alfort, 7 Avenue du Général de Gaulle, 94704 Maisons-Alfort Cedex, Francec.vergari@gmail.com

Philippe Pourcelot, Laurène Holden, Bérangère Ravary-Plumioën, Nathalie Crevier-Denoix

USC INRA-ENVA, Biomécanique et Pathologie Locomotrice du Cheval, Ecole Nationale Vétérinaire d’Alfort, 7 Avenue du Général de Gaulle, 94704 Maisons-Alfort Cedex, France

Pascal Laugier

UPMC, Univ Paris 6, UMR CNRS7623, LIP, Paris F-75005, France

David Mitton

Université de Lyon, F-69622, Lyon, France; INRETS, UMR_T9406, LBMC; Université Lyon 1

1

Corresponding author.

J Biomech Eng 132(10), 105001 (Sep 10, 2010) (7 pages) doi:10.1115/1.4002374 History: Received January 25, 2010; Revised June 18, 2010; Posted August 16, 2010; Published September 10, 2010

## Abstract

Measure of the cross-sectional area (CSA) of biological specimens is a primary concern for many biomechanical tests. Different procedures are presented in literature but besides the fact that noncontact techniques are required during mechanical testing, most of these procedures lack accuracy or speed. Moreover, they often require a precise positioning of the specimen, which is not always feasible, and do not enable the measure of the same section during tension. The objective of this study was to design a noncontact, fast, and accurate device capable of acquiring CSA of specimens mounted on a testing machine. A system based on the horizontal linear displacement of two charge-coupled device reflectance laser devices next to the specimen, one for each side, was chosen. The whole measuring block is mounted on a vertical linear guide to allow following the measured zone during sample tension (or compression). The device was validated by measuring the CSA of metallic rods machined with geometrical shapes (circular, hexagonal, semicircular, and triangular) as well as an equine superficial digital flexor tendon (SDFT) in static condition. We also performed measurements during mechanical testing of three SDFTs, obtaining the CSA variations until tendon rupture. The system was revealed to be very fast with acquisition times in the order of 0.1 s and interacquisition time of about 1.5 s. Measurements of the geometrical shapes yielded mean errors lower than 1.4% ($n=20$ for each shape) while the tendon CSA at rest was $90.29±1.69 mm2$$(n=20)$. As for the tendons that underwent tension, a mean of 60 measures were performed for each test, which lasted about 2 min until rupture (at 20 mm/min), finding CSA variations linear with stress $(R2>0.85)$. The proposed device was revealed to be accurate and repeatable. It is easy to assemble and operate and capable of moving to follow a defined zone on the specimen during testing. The system does not need precise centering of the sample and can perform noncontact measures during mechanical testing; therefore, it can be used to measure variations of the specimen CSA during a tension (or compression) test in order to determine, for instance, the true stress and transverse deformations.

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## Figures

Figure 1

(a) Lateral view and (b) top view of the device. Characteristic distances are reported: DX and DY are, respectively, the distance between lasers and the offset imposed to avoid mutual interference; DL1 and DL2 are the distances measured by each laser between itself and the specimen surface.

Figure 2

Photo of the device in situ. (P) potentiometer, (L) measuring lasers, (Lp) laser pointer, (S) synchronization plate, (R) geometrical rods, and (B) steel base placed on the machine working plane for supporting purposes.

Figure 3

Orientation of the specimen. (a) The steep angle between the specimen border and laser 1 beam deteriorates the measure while a good orientation (b) optimizes the result.

Figure 4

Typical cross-sectional shapes obtained with the device: (a) circular shape, (b) hexagon, (c) semicircle, and (d) triangle

Figure 5

Cross-section of an equine superficial digital flexor tendon acquired by ultrasonography (a), digital photography (b), and linear laser scanner proposed in present article (c)

Figure 6

Cross-sectional area variations with stress of three superficial digital flexor tendons during uniaxial tension. Tendon Nos. 1, 2, and 3 failed at 140.88 MPa, 104.99 MPa, and 124.25 MPa (corresponding to 16.03 kN, 12.41 kN, and 15.23 kN), respectively. In terms of percentage variation of initial area, linear regressions have slopes of −0.08% MPa(R2=0.87), −0.10% MPa(R2=0.85), and −0.06% MPa(R2=0.93), respectively.

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