Name: performing microscope-mounted y-shaped cutting tests
Uploaded: 2023-01-20T12:45:00
Description: Watch this Scientific Journal Video about Performing Microscope-Mounted Y-Shaped Cutting Tests at JoVE.com

We would like to thank Dr. James Phillips, Dr. Amy Wagoner-Johnson, Alexandra Spitzer, and Amir Ostadi for their advice on this work. Funding came from the start-up grant provided by the Department of Mechanical Science and Engineering at the University of Illinois Urbana-Champaign. M. Guerena, J. C. Peng, M. Schmid, and C. Walsh all received senior design credit for their work on this project.

1. Adjustment and manufacturing of modifiable and consumable parts
<ol>
	<li>Use a laser cutter or 3D printer to manufacture disposable ABS or acrylic tabs that fit within the width of the sample legs, B1 and B2 (7.5 mm x 7.5 mm for a 1.5 cm x 7 cm x 3 mm sample) (Figure 1B and Figure 2D). Two tabs are needed for each test, one for each leg.</li>
	<li>Razor blade clip 
	NOTE: The exact dimensions of the required razor blade clip depend on...

<ol>
	<li>Long, R., Hui, C. -. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crack+tip+fields+in+soft+elastic+solids+subjected+to+large+quasi-static+deformation+-+A+review.">Crack tip fields in soft elastic solids subjected to large quasi-static deformation - A review.</a> Extreme Mechanics Letters. 4, 131-155 (2015).</li><li>Slootman, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantifying+rate-and+temperature-dependent+molecular+damage+in+elastomer+fracture.">Quantifying rate-and temperature-dependent molecular damage in elastomer fracture.</a> Physical Review X. 10, 041045 (2020).</li><li>Zhao, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Soft+materials+by+design:+Unconventional+polymer+networks+give+extreme+properties.">Soft materials by design: Unconventional polymer networks give extreme properties.</a> Chemical Review. 121 (8), 4309-4372 (2021).</li><li>Mzabi, S., Berghezan, D., Roux, S., Hild, F., Creton, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+critical+local+energy+release+rate+criterion+for+fatigue+fracture+of+elastomers.">A critical local energy release rate criterion for fatigue fracture of elastomers.</a> Journal of Polymer Science Part B: Polymer Physics. 49 (21), 1518-1524 (2011).</li><li>Chen, Y., Mellot, G., Van Luijk, D., Creton, C., Sijbesma, R. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanochemical+tools+for+polymer+materials.">Mechanochemical tools for polymer materials.</a> Chemical Society Reviews. 50, 4100-4140 (2021).</li><li>Hui, C. -. Y., Jagota, A., Bennison, S. J., Londono, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crack+blunting+and+the+strength+of+soft+elastic+solids.">Crack blunting and the strength of soft elastic solids.</a> Proceedings of the Royal Society A Mathematical, Physical and Engineering Science. 459 (2034), 1489-1516 (2003).</li><li>Zhang, B., Hutchens, S. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+relationship+between+cutting+and+tearing+in+soft+elastic+solids.">On the relationship between cutting and tearing in soft elastic solids.</a> Soft Matter. 17, 6728-6741 (2021).</li><li>Lake, G. J., Yeoh, O. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+rubber+cutting+resistance+in+the+absence+of+friction.">Measurement of rubber cutting resistance in the absence of friction.</a> International Journal of Fracture. 14, 509-526 (1978).</li><li>Zhang, B., Shiang, C. -. S., Yang, S. J., Hutchens, S. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Y-shaped+cutting+for+the+systematic+characterization+of+cutting+and+tearing.">Y-shaped cutting for the systematic characterization of cutting and tearing.</a> Experimental Mechanics. 59, 517-529 (2019).</li><li>Rivlin, R. S., Thomas, A. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rupture+of+rubber.+I.+Characteristic+energy+for+tearing.">Rupture of rubber. I. Characteristic energy for tearing.</a> Journal of Polymer Science. 10 (3), 291-318 (1953).</li><li>Elices, M., Guinea, G. V., G&#243;mez, J., Planas, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+cohesive+zone+model:+Advantages,+limitations+and+challenges.">The cohesive zone model: Advantages, limitations and challenges.</a> Engineering Fracture Mechanics. 69 (2), 137-163 (2002).</li><li>Taylor, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Theory of Critical Distances. , (2007).</li><li>Williams, J. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stress+at+a+distance+fracture+criteria+and+crack+self-blunting+in+rubber.">Stress at a distance fracture criteria and crack self-blunting in rubber.</a> International Journal of Non-Linear Mechanics. 68, 33-36 (2015).</li><li>Talamini, B., Mao, Y., Anand, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Progressive+damage+and+rupture+in+polymers.">Progressive damage and rupture in polymers.</a> Journal of the Mechanics and Physics of Solids. 111, 434-457 (2018).</li><li>Long, R., Hui, C. -. Y., Gong, J. P., Bouchbinder, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+fracture+of+highly+deformable+soft+materials:+A+tale+of+two+length+scales.">The fracture of highly deformable soft materials: A tale of two length scales.</a> Annual Review of Condensed Matter Physics. 12, 71-94 (2021).</li><li>Gent, A. N., Wang, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cutting+resistance+of+polyethylene.">Cutting resistance of polyethylene.</a> Journal of Polymer Science: Part B: Polymer Physics. 34 (13), 2231-2237 (1996).</li><li>Chen, X., Nadiarynkh, O., Plotnikov, S., Campagnola, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Second+harmonic+generation+microscopy+for+quantitative+analysis+of+collagen+fibrillar+structure.">Second harmonic generation microscopy for quantitative analysis of collagen fibrillar structure.</a> Nature Protocols. 7, 654-669 (2015).</li><li>Pan, B., Qian, K., Xie, H., Asundi, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-dimensional+digital+image+correlation+for+in-plane+displacement+and+strain+measurement:+A+review.">Two-dimensional digital image correlation for in-plane displacement and strain measurement: A review.</a> Measurements Science and Technology. 20 (6), 062001 (2009).</li></ol>

The horizontal, Y-shaped cutting apparatus reported here enables in situ imaging capabilities along with improved ease-of-use for this failure technique. The apparatus includes a modular/portable design for quick mounting/unmounting from a microscope and continuous, pre-aligned leg angle adjustment. All the CAD files, required materials, and procedures have been included to facilitate the implementation of this method. In many instances (blade holders, sample holder, load-cell mount, mounting frame), the 3D-prin...

Nonlinear continuum mechanics has provided a critical lens through which to understand the concentration of energy that leads to failure in soft solids1. However, the accurate prediction of this failure also requires descriptions of the microstructural characteristics that contribute to new surface creation at the crack tip2,3. One method to approach such descriptions is through in situ visualization of the crack tip during failure4,5. However, crack blunting in typical far-field fracture tests makes the acquisition of in situ data challenging by spreading out the highly deformed material, potentially outside the microscope&#39;s field of view6. Y-shaped cutting offers a unique alternative for microstructural visualization because it concentrates the region of large deformation at the tip of a blade7. Furthermore, previous work from our group demonstrates that this unique experimental approach can provide insight into the differences in failure response between far-field tearing and contact-mediated loading conditions7.
The Y-shaped cutting method used in the apparatus presented here was first described decades ago as a cutting method for natural rubber8. The method consists of a fixed blade push-cutting through a preloaded Y-shaped test piece. At the intersection of the &#34;Y&#34; is the crack tip, which is created prior to testing by splitting a portion of a rectangular piece into two equal &#34;legs&#34; (Figure 1B and Figure 2D). The primary advantages of this cutting method include the reduction of frictional contributions to the measured cutting energy, the variable blade geometry (i.e., constraint of the crack tip geometry), the control of the failure rate (via the sample displacement rate), and the separate tuning of the cutting, C, and tearing, T, energy contributions to the total energy Gcut (i.e., altering the failure energy in excess of a cutting threshold)8. The latter contributions are expressed in a simple, closed-form expression for the cutting energy9
<img alt="Equation 1" src="/files/ftp_upload/64546/64546eq01v3.jpg" style="margin: auto;" /> Eqn (1)
which uses experimentally selected parameters, including sample thickness, t, average leg strain, <img alt="Equation 2" src="/files/ftp_upload/64546/64546eq02v2.jpg" style="margin: auto;" />, preload force, fpre, and the angle between the legs and the cutting axis, &#952;. The cutting force, fcut, is measured with the apparatus as detailed in Zhang et al.9. Notably, the apparatus presented here includes a new, simple, and accurate mechanism for tuning the leg angle, &#952;, and ensuring the sample is centered. While both features are critical for a microscope-mounted setup, the mechanism may benefit future vertical implementations of the Y-shaped cutting test as well by increasing the ease of use.
Progress in determining the appropriate failure criteria for soft solids has been ongoing since the early success of sample-independent fracture geometries introduced by Rivlin and Thomas10. Critical energy release rates10, cohesive zone laws11, and various forms of stress- or energy-at-a-distance approaches12,13,14 have been used. Recently, Zhang and Hutchens leveraged the latter approach, demonstrating that Y-shaped cutting with sufficiently small radius blades could yield threshold failure conditions for soft fracture7: a threshold failure energy and a threshold length scale for failure that ranges from tens to hundreds of nanometers in homogeneous, highly-elastic polydimethylsiloxane (PDMS). These results were combined with continuum modeling and scaling theory to develop a relationship between cutting and tearing in these materials, thus demonstrating the utility of Y-shaped cutting for providing insights into all modes of soft failure. However, the behavior of many material classes, including dissipative and composite materials, remains unexplored. It is anticipated that many of these will exhibit microstructure-governed effects at length scales above the wavelength of visible light. Therefore, an apparatus was designed in this study that allows for the close visual characterization of these effects during Y-shaped cutting for the first time (e.g., in composites, including soft tissues, or of dissipative processes, anticipated on the micrometer to millimeter length scales15).

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
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			<td>Buy Parts</td>
			<td></td>
			<td></td>
			<td></td>
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		<tr>
			<td>1&#34; OD Pulley</td>
			<td>McMaster Carr</td>
			<td>3434T75</td>
			<td>Pulley for Wire Rope (Larger)</td>
		</tr>
		<tr>
			<td>100 g Micro Load Cell</td>
			<td>RobotShop</td>
			<td>RB-Phi-203</td>
			<td></td>
		</tr>
		<tr>
			<td>1K Resistor</td>
			<td>Digi-Key</td>
			<td>CMF1.00KFGCT-ND</td>
			<td>1 kOhms &#177;1% 1 W Through Hole Resistor Axial Flame Retardant Coating, Moisture Resistant, Safety Metal Film</td>
		</tr>
		<tr>
			<td>1M Resistor</td>
			<td>Digi-Key</td>
			<td>RNF14FAD1M00</td>
			<td>1 MOhms &#177;1% 0.25 W, 1/4 W Through Hole Resistor Axial Flame Retardant Coating, Safety Metal Film</td>
		</tr>
		<tr>
			<td>3/8&#34; OD Pulley</td>
			<td>McMaster Carr</td>
			<td>3434T31</td>
			<td>Pulley for Wire Rope</td>
		</tr>
		<tr>
			<td>4&#34; Clear Protractor with Easy Read Markings</td>
			<td>S&#38;S Worldwide</td>
			<td>LR3023</td>
			<td></td>
		</tr>
		<tr>
			<td>Breadboard</td>
			<td>ECEB</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>IC OPAMP ZERO-DRIFT 2 CIRC 8DIP</td>
			<td>Digi-Key</td>
			<td>LTC1051CN8#PBF-ND</td>
			<td></td>
		</tr>
		<tr>
			<td>M2 x 0.4 mm Nut</td>
			<td>McMaster Carr</td>
			<td>90592A075</td>
			<td>Steel Hex Nut</td>
		</tr>
		<tr>
			<td>M2 x 0.4 mm x 25 mm</td>
			<td>McMaster Carr</td>
			<td>91292A032</td>
			<td>18-8 Stainless Steel Socket Head Screw</td>
		</tr>
		<tr>
			<td>M2 x 0.4 mm x 8 mm</td>
			<td>McMaster Carr</td>
			<td>91292A832</td>
			<td>18-8 Stainless Steel Socket Head Screw</td>
		</tr>
		<tr>
			<td>M3 x 0.5 mm x 15 mm</td>
			<td>McMaster Carr</td>
			<td>91290A572</td>
			<td>Black-Oxide Alloy Steel Socket Head Screw</td>
		</tr>
		<tr>
			<td>M3 x 0.5 mm x 16 mm</td>
			<td>McMaster Carr</td>
			<td>91294A134</td>
			<td>Black-Oxide Alloy Steel Hex Drive Flat Head Screw</td>
		</tr>
		<tr>
			<td>M3 x 0.5 mm, 4 mm High</td>
			<td>McMaster Carr</td>
			<td>90576A102</td>
			<td>Medium-Strength Steel Nylon-Insert Locknut</td>
		</tr>
		<tr>
			<td>M4 x 0.7 mm Nut</td>
			<td>McMaster Carr</td>
			<td>90592A090</td>
			<td>Steel Hex Nut</td>
		</tr>
		<tr>
			<td>M4 x 0.7 mm x 15 mm</td>
			<td>McMaster Carr</td>
			<td>91290A306</td>
			<td>Black-Oxide Alloy Steel Socket Head Screw</td>
		</tr>
		<tr>
			<td>M4 x 0.7 mm x 16 mm</td>
			<td>McMaster Carr</td>
			<td>91294A194</td>
			<td>Black-Oxide Alloy Steel Hex Drive Flat Head Screw</td>
		</tr>
		<tr>
			<td>M4 x 0.7 mm x 18 mm</td>
			<td>McMaster Carr</td>
			<td>91290A164</td>
			<td>Black-Oxide Alloy Steel Socket Head Screw</td>
		</tr>
		<tr>
			<td>M4 x 0.7 mm x 20 mm</td>
			<td>McMaster Carr</td>
			<td>91290A168</td>
			<td>Black-Oxide Alloy Steel Socket Head Screw</td>
		</tr>
		<tr>
			<td>M4 x 0.7 mm x 20 mm</td>
			<td>McMaster Carr</td>
			<td>92581A270</td>
			<td>Stell Raised Knurled-Head Thumb Screw</td>
		</tr>
		<tr>
			<td>M4 x 0.7 mm x 30 mm</td>
			<td>McMaster Carr</td>
			<td>91290A172</td>
			<td>Black-Oxide Alloy Steel Socket Head Screw</td>
		</tr>
		<tr>
			<td>M4 x 0.7 mm x 50 mm</td>
			<td>McMaster Carr</td>
			<td>91290A193</td>
			<td>Black-Oxide Alloy Steel Socket Head Screw</td>
		</tr>
		<tr>
			<td>M4 x 0.7 mm, 5 mm High</td>
			<td>McMaster Carr</td>
			<td>94645A101</td>
			<td>High-Strength Steel Nylon-Insert Locknut</td>
		</tr>
		<tr>
			<td>M5 x 0.8 mm Nut</td>
			<td>McMaster Carr</td>
			<td>90592A095</td>
			<td>Steel Hex Nut</td>
		</tr>
		<tr>
			<td>M5 x 0.8 mm x 16 mm</td>
			<td>McMaster Carr</td>
			<td>91310A123</td>
			<td>High-Strength Class 10.9 Steel Hex Head Screw</td>
		</tr>
		<tr>
			<td>M5 x 0.8 mm x 35 mm</td>
			<td>McMaster Carr</td>
			<td>91290A195</td>
			<td>Black-Oxide Alloy Steel Socket Head Screw</td>
		</tr>
		<tr>
			<td>M5 x 0.8 mm, 13 mm Head Diameter</td>
			<td>McMaster Carr</td>
			<td>96445A360</td>
			<td>Flanged Knurled-Head Thumb Nut</td>
		</tr>
		<tr>
			<td>M5 x 0.8 mm, 5 mm High</td>
			<td>McMaster Carr</td>
			<td>90576A104</td>
			<td>Medium-Strength Steel Nylon-Insert Locknut</td>
		</tr>
		<tr>
			<td>Solidworks</td>
			<td>Dassault Systemes</td>
			<td></td>
			<td>CAD software</td>
		</tr>
		<tr>
			<td>Wiring Kit</td>
			<td>ECEB</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>XYZ Axis Manual Precision Linear Stage 60 mm x 60 mm Trimming Bearing Tuning Platform Sliding Table</td>
			<td>OpticsFocus</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Make Parts</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Angle adjustment system- arm</td>
			<td>3D Printing</td>
			<td></td>
			<td>solidworks: arms_arm_single.SLDPRT 
			QTY: 2 
			Setting: Fast/0.2 mm layer height</td>
		</tr>
		<tr>
			<td>Angle adjustment system- arms stationary</td>
			<td>3D Printing</td>
			<td></td>
			<td>solidworks: arms_stationary.SLDPRT 
			QTY: 1 
			Setting: Fast/0.2 mm layer height</td>
		</tr>
		<tr>
			<td>Angle adjustment system- link</td>
			<td>3D Printing</td>
			<td></td>
			<td>solidworks: arms_arm_link.SLDPRT 
			QTY: 2 
			Setting: Fast/0.2 mm layer height</td>
		</tr>
		<tr>
			<td>Angle adjustment system- slider</td>
			<td>3D Printing</td>
			<td></td>
			<td>solidworks: arms_slider.SLDPRT 
			QTY: 1 
			Setting: Fast/0.2 mm layer height</td>
		</tr>
		<tr>
			<td>Angle adjustment system- spacer</td>
			<td>3D Printing</td>
			<td></td>
			<td>solidworks: arms_front_spacer.SLDPRT 
			QTY: 1 
			Setting: Fast/0.2 mm layer height</td>
		</tr>
		<tr>
			<td>Clip- Blade clip</td>
			<td>3D Printing</td>
			<td></td>
			<td>solidworks: Blade clip.SLDPRT 
			QTY: 1 
			Setting: Fine/0.1 mm layer height</td>
		</tr>
		<tr>
			<td>Clip- Blade clip mount</td>
			<td>3D Printing</td>
			<td></td>
			<td>solidworks: Blade clip mount.SLDPRT 
			QTY: 1 
			Setting: Fine/0.1 mm layer height</td>
		</tr>
		<tr>
			<td>Frame arm</td>
			<td>3D Printing</td>
			<td></td>
			<td>solidworks: frame arm.SLDPRT 
			QTY: 2 
			Setting: Fast/0.2 mm layer height</td>
		</tr>
		<tr>
			<td>Mounting platform</td>
			<td>Laser Cut Acrylic</td>
			<td></td>
			<td>solidworks: mounting platform.SLDPRT 
			QTY: 1</td>
		</tr>
		<tr>
			<td>Pulley arm (left)</td>
			<td>3D Printing</td>
			<td></td>
			<td>solidworks: pulley arm_Mirror.SLDPRT 
			QTY: 1 
			Setting: Fast/0.2 mm layer height</td>
		</tr>
		<tr>
			<td>Pulley arm (right)</td>
			<td>3D Printing</td>
			<td></td>
			<td>solidworks: pulley arm.SLDPRT 
			QTY: 1 
			Setting: Fast/0.2 mm layer height</td>
		</tr>
		<tr>
			<td>Sample holder and tab- Clamp</td>
			<td>3D Printing</td>
			<td></td>
			<td>solidworks: Clamp.SLDPRT 
			QTY: 1 
			Setting: Fast/0.2 mm layer height</td>
		</tr>
		<tr>
			<td>Sample holder and tab- Sample holder</td>
			<td>3D Printing</td>
			<td></td>
			<td>solidworks: Sample holder.SLDPRT 
			QTY: 1 
			Setting: Fast/0.2 mm layer height</td>
		</tr>
		<tr>
			<td>Sample holder and tab- Tab</td>
			<td>3D Printing</td>
			<td></td>
			<td>solidworks: Tab.SLDPRT 
			QTY: 2 per test 
			Setting: Fine/0.1 mm layer height, no brim</td>
		</tr>
		<tr>
			<td>Vertical adjust system- Inner slide</td>
			<td>3D Printing</td>
			<td></td>
			<td>solidworks: Inner slide.SLDPRT 
			QTY: 1 
			Setting: Fast/0.2 mm layer height</td>
		</tr>
		<tr>
			<td>Vertical adjust system- Outer slide</td>
			<td>3D Printing</td>
			<td></td>
			<td>solidworks: Outer slide.SLDPRT 
			QTY: 1 
			Setting: Fast/0.2 mm layer height</td>
		</tr>
	</tbody>
</table>

performing microscope-mounted y-shaped cutting tests

Y-shaped cutting has recently been shown to be a promising method by which to understand the threshold length scale and failure energy of a material, as well as its failure response in the presence of excess deformation energy. The experimental apparatus used in these studies was vertically oriented and required cumbersome steps to adjust the angle between the Y-shaped legs. The vertical orientation prohibits visualization in standard optical microscopes. This protocol presents a Y-shaped cutting apparatus that mounts horizontally over an existing inverted microscope stage, can be adjusted in three dimensions (X-Y-Z) to fall within the objective&#39;s field of view, and allows easy modification of the angle between the legs. The latter two features are new for this experimental technique. The presented apparatus measures the cutting force within 1 mN accuracy. When testing polydimethylsiloxane (PDMS), the reference material for this technique, a cutting energy of 132.96 J/m2 was measured (32&#176; leg angle, 75 g preload) and found to fall within the error of previous measurements taken with a vertical setup (132.9 J/m2 &#177; 3.4 J/m2). The approach applies to soft synthetic materials, tissues, or bio-membranes and may provide new insights into their behavior during failure. The list of parts, CAD files, and detailed instructions in this work provide a roadmap for the easy implementation of this powerful technique.

The parameters used during step 4 and step 6 and the data gathered during step 6 and step 9 combine to yield the cutting energy of the sample. According to Eqn. 1, the determination of the cutting energy requires the following parameters: sample thickness, t, preload force, fpre, and the angle between the legs and the cutting axis, &#952;. The following data are also required: the cutting force, fcut, and the average leg strain, <img alt="Equation 2" src="/files/ftp_upload...

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Performing Microscope-Mounted Y-Shaped Cutting Tests

Y-shaped cutting measures fracture-relevant length scales and energies in soft materials. Previous apparatuses were designed for benchtop measurements. This protocol describes the fabrication and use of an apparatus that orients the setup horizontally and provides the fine positioning capabilities necessary for in situ viewing, plus failure quantification, via an optical microscope.

Y-shaped cutting has recently been shown to be a promising method by which to understand the threshold length scale and failure energy of a material, as ...

Y-shaped cutting measures failure energy and a critical surface creation link scale in soft solids. Incorporating this technique into a microscope facilitates unraveling the microstructural mechanisms that govern these quantities. In contrast to the large planted crack typical of front-wheel loading, this protocol uses plate-induced stretch localization to reduce the field-of-view needed to image the interior failure process.The approach may provide insight into the failure of soft synthetic materials and biological soft tissues. To begin, replace the original stage-mounted slide holder with a custom sample holder and attach the assembly to the microscope. Set the angle of the cup by loosening the angle adjust thumbscrew and then moving the linear slide.Set the angle after measuring it with a protractor and tighten the angle adjust thumb screw. The angle between the leg and the sample midplane theta can be adjusted from 8 to 45 degrees. Set up the two vertical pulleys behind the apparatus.Prepare a thin rectangular sample of polydimethylsiloxane, or PDMS, by either cutting it from a larger sheet or using a mold of the correct dimensions. The dimensions may vary, but a width of 1 1/2 centimeters or less for a sample with a thickness of three millimeters or less is recommended to start. Use a razor blade to cut the sample three centimeters lengthwise along the center line to create the Y-shaped sample.This link may vary but the legs should be long enough to accommodate the tabs, yet short enough to leave an uncut sample for measurement. Using a marker or ink, place two marks centered and separated by approximately one centimeter on each of the thin legs and the body of the sample to measure the applied stretch in each of the three sample legs under load. Use adhesive-like cyanoacrylate glue to attach a 3D-printed or laser-cut tab to the end of each leg.Measure and cut two lengths of thin fishing line. Approximately 30 centimeters of line is needed for internal routing through the mechanism to the external set of pulleys. Attach five-gram weighing plates to the end of the lines passing through the external pulleys and tie the other end to the tab on each leg.Clamp the base of the sample using the sample holder thumbscrew and route the line for each leg through each side of the pulley system. Take a picture of the sample from the top while the sample is under negligible weight by holding a camera against the underside of the angle adjustment mechanism. Make sure the camera is parallel to the sample plane to minimize off-angle effects.Add the desired preload weight of 75 grams to both ends of the fishing line near the external pulleys. Increase this quantity to 150 grams or decrease it to 50 grams to change the tearing contribution if desired for this combination of material and sample geometry. Align the fishing line from the lowest pulley with the Z plane of the sample legs using the Z component of the three-way micro adjustment stage.Take a second picture of the sample after the weight is added. Approximately position the anticipated blade tip close to the objective's field-of-view. Place the razor blade into its corresponding blade clip and secure the blade in place with a set screw.Slide this clipped razor blade into the blade clip mount attached to the load cell. Select the 2.5x microscope objective or as high as 20x, if closer images are desired, and use the transmitted light setting, augmenting the light behind the sample if needed. With the blade in place, focus the microscope on the nearest surface of the blade using the vertical adjust system if necessary to bring the tip to the appropriate working distance for the objective.Carefully align the razor blade within the microscope's field-of-view using only the X and Y directions of the three-way microadjustment stage. Focus the microscope on the sample and align the crack tip with the razor blade by translating the microscope X/Y stage. This ensures that the midplane of the sample aligns with the midplane of the angle adjustment mechanism.Open the code used for the load cell data acquisition and start recording the load cell data by clicking the Start Recording button. Translate the sample toward the razor blade for one centimeter or more at constant velocity using microscope stage control. Simultaneously gather images using the microscope's imaging interface.When the microscope X/Y stage stops, click the Stop Recording button to stop recording the data and automatically save a text file of the load and time response. The force-time curve for polydimethylsiloxane using an ultra sharp blade is shown here. The elastic loading, cut initiation, steady-state cutting, and unloading regions of the curve are labeled in the graph.This data illustrates a high initial force, as is typically required for cut initiation, followed by a constant force, indicating steady-state cutting. The cutting force is the maximum value of the force within this steady-state regime. The red circles shown here correspond to specific images obtained by the microscope.A yellow circle has been added to facilitate the observation of the speckle pattern motion, and these numbers indicate image timestamps and seconds. The measured steady-state cutting force combined with the experimental testing parameters of leg angle theta, sample thickness T, preload f of pre, and blade radius yield the steady-state cutting energy according to the equation shown. Here, we successfully replicate the cutting energy previously reported in the literature for these conditions.By incorporating Y-shaped cutting into a microscope, we enable the quantification of microstructural contributions to soft-solid and soft tissue failure via fluorescent probes, autofluorescence, and full-field strength techniques.

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