Name: A Testing Platform for Durability Studies of Polymers and Fiber-reinforced Polymer Composites under Concurrent Hygrothermo-mechanical Stimuli (Video) | JoVE Journal
Uploaded: 2014-12-11T15:00:00.000+00:00
Duration: 7 min 15 s
Description: Learn a low-cost testing method for polymer composite durability under concurrent hydrothermal and mechanical loads using a flexible platform. This approach improves material design and safety for engineering structures.

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5 minutes

The authors thank Destiny Garcia, Serena Ferraro, Erik Quiroz and Steven Kern (Advanced Composites Research, Engineering and Science laboratory) for their help in designing and manufacturing the test setup. Shawn Malone, Michael Akahori, David Kehlet (Engineering Fabrication Lab) are acknowledged for their suggestions and assistance in the machining process. The support of the National Science Foundation (collaborative grant CMMI-1265691 and its REU supplement) and the Office of Naval Research (N00014-13-1-0604 to A. Muliana, Texas &#38;M University (Principal Investigator), and V. La Saponara, managed by program director Yapa Rajapakse) are gratefully appreciated.

1. Loading the Specimens
<ol>
	<li>Raise the lid of the tank and rest it upon the side supports (Figure 4).</li>
	<li>Place the specimen in the U-bolt, and ensure that the cross bar is making contact at the center of the specimen.</li>
	<li>Rest the ends of the specimen on the aluminum supports hanging from the lid. The ends of the specimens should have 5-10 mm of overhang.</li>
	<li>Repeat steps 1.2-1.4 for all of the specimens that will be tested.</li>
	<li>Remove the lid supports, lower lid, and make sure that the lid is seated on the lip of the tank.</li>
	<li>Apply the desired force by adding weights to the steel rod next to the outer pulley.</li>
</ol>
2. Measuring Displacement
<ol>
	<li>Ensure that the string potentiometer line is pulled taut.</li>
	<li>Using a digital multimeter, measure the resistance across the outer pins of the potentiometer (Figure 3), with black to Pin 1 and red to Pin 3, and record the reading.</li>
	<li>Convert the resistance reading into a displacement reading by computing the calibration factor (in this case, 1 k&#8486; corresponds to a 64.895 mm displacement).</li>
	<li>Repeat steps 2.1-2.3 for each specimen.</li>
</ol>
3. Weighing the Specimens
<ol>
	<li>Before beginning the weighing procedure, record the displacement data and prepare an interim holding chamber filled with the testing fluid at RT, as per ASTM D522931, or the appropriate testing standard.</li>
	<li>Remove the slotted weights from the ends of the steel cables.</li>
	<li>Raise the lid of the tank and rest it upon the side supports.</li>
	<li>Remove the specimen and place it into the prepared interim holding chamber. Repeat this step for all of the specimens.</li>
	<li>Remove the specimens and dry them individually using a microfiber cloth in order to remove excess fluid.</li>
	<li>Place the specimen on a high-precision scale and record the data reading.</li>
	<li>Repeat steps 3.5-3.6 for all specimens and then follow Protocol Step 1.</li>
</ol>

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<li>Hollaway, L. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+review+of+the+present+and+future+utilization+of+FRP+composites+in+the+civil+infrastructure+with+reference+to+their+important+in-service+properties%5BTitle%5D)+AND+%22Constr+Build+Mater%22%5BJournal%5D)">A review of the present and future utilization of FRP composites in the civil infrastructure with reference to their important in-service properties.</a> Constr Build Mater. 24, 2419-2445 (2010).</li>
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<li>Albanilla, M. A., Li, Y., Karbhari, V. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Durability+characterization+of+wet+layup+graphite%2Fepoxy+composites+used+in+external+strengthening%5BTitle%5D)+AND+%22Compos+Part+B-Eng%22%5BJournal%5D)">Durability characterization of wet layup graphite/epoxy composites used in external strengthening.</a> Compos Part B-Eng. 37, 200-212 (2006).</li>
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<li>Zhou, J., Lucas, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Hygrothermal+effects+of+epoxy+resin.+Part+I%3A+the+nature+of+water+in+epoxy%5BTitle%5D)+AND+%22Polymer%22%5BJournal%5D)">Hygrothermal effects of epoxy resin. Part I: the nature of water in epoxy.</a> Polymer. 40, 5505-5512 (1999).</li>
<li>Abot, J. L., Yasmin, A., Daniel, I. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Hygroscopic+Behavior+of+Woven+Carbon-Epoxy+Composites%5BTitle%5D)+AND+%22J.+Reinf.+Plast.+Comp%22%5BJournal%5D)">Hygroscopic Behavior of Woven Carbon-Epoxy Composites.</a> J. Reinf. Plast. Comp. 24, 195-207 (2005).</li>
<li>LaPlante, G., Ouriadov, A. V., Lee-Sullivan, P., Balcom, B. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Anomalous+Moisture+Diffusion+in+an+Epoxy+Adhesive%5BTitle%5D)+AND+%22J.+Appl.+Polym.+Sci%22%5BJournal%5D)">Anomalous Moisture Diffusion in an Epoxy Adhesive.</a> J. Appl. Polym. Sci. 109, 1350-1359 (2008).</li>
<li>Weitsman, Y. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Anomalous+fluid+sorption+in+polymeric+composites+and+its+relation+to+fluid-induced+damage%5BTitle%5D)+AND+%22Compos.+Part+A+%E2%80%93Appl.+Sci%22%5BJournal%5D)">Anomalous fluid sorption in polymeric composites and its relation to fluid-induced damage.</a> Compos. Part A –Appl. Sci. 37, 617-623 (2006).</li>
<li>Karbhari, V. M., Ghosh, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Comparative+durability+evaluation+of+ambient+temperature+cured+externally+CFRP+and+GFRP+composiste+systems+for+repair+of+bridges%5BTitle%5D)+AND+%22Compos.+Part+A+%E2%80%93Appl.+Sci%22%5BJournal%5D)">Comparative durability evaluation of ambient temperature cured externally CFRP and GFRP composiste systems for repair of bridges.</a> Compos. Part A –Appl. Sci. 40, 1353-1363 (2009).</li>
<li>Neumann, S., Marom, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Free-volume+dependent+moisture+diffusion+under+stress+in+composite+materials%5BTitle%5D)+AND+%22J.+Mater.+Sci%22%5BJournal%5D)">Free-volume dependent moisture diffusion under stress in composite materials.</a> J. Mater. Sci. 21, 26-30 (1986).</li>
<li>Wan, Y. Z., Wang, Y. L., Huang, Y., He, B. M., Han, K. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Hygrothermal+aging+behaviour+of+VARTMed+three-dimensional+braided+carbon-epoxy+composites+under+external+stresses%5BTitle%5D)+AND+%22Compos.+Part+A+%E2%80%93Appl.+Sci%22%5BJournal%5D)">Hygrothermal aging behaviour of VARTMed three-dimensional braided carbon-epoxy composites under external stresses.</a> Compos. Part A –Appl. Sci. 36, 1102-1109 (2005).</li>
<li>Helbling, C. S., Karbhari, V. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Investigation+of+the+Sorption+and+Tensile+Response+of+Pultruded+E-Glass%2FVinylester+Composites+Subjected+to+Hygrothermal+Exposure+and+Sustained%5BTitle%5D)+AND+%22J.+Reinf.+Plast.+Comp%22%5BJournal%5D)">Investigation of the Sorption and Tensile Response of Pultruded E-Glass/Vinylester Composites Subjected to Hygrothermal Exposure and Sustained.</a> J. Reinf. Plast. Comp. 27, 613-638 (2008).</li>
<li>Kasturiarachchi, K. A., Pritchard, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Water+absorption+of+glass%2Fepoxy+laminates+under+bending+stresses%5BTitle%5D)+AND+%22Composites%22%5BJournal%5D)">Water absorption of glass/epoxy laminates under bending stresses.</a> Composites. 14, 244-250 (1983).</li>
<li>Abdel-Magid, B., Ziaee, S., Gass, K., Schneider, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+combined+effects+of+load%2C+moisture+and+temperature+on+the+properties+of+E-glass%2Fepoxy+composites%5BTitle%5D)+AND+%22Compos+Struct%22%5BJournal%5D)">The combined effects of load, moisture and temperature on the properties of E-glass/epoxy composites.</a> Compos Struct. 71, 320-326 (2005).</li>
<li>Ellyin, F., Rohrbarcher, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+Influence+of+Aqueous+Environment%2C+Temperature+and+Cyclic+Loading+on+Glass-Fibre%2FEpoxy+Composite+Laminates%5BTitle%5D)+AND+%22J+Reinf+Plast+Comp%22%5BJournal%5D)">The Influence of Aqueous Environment, Temperature and Cyclic Loading on Glass-Fibre/Epoxy Composite Laminates.</a> J Reinf Plast Comp. 22, 615-636 (2003).</li>
<li>Earl, J. S., Dulieu-Barton, J. M., Shenoi, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Determination+of+hygrothermal+ageing+effects+in+sandwich+construction+joints+using+thermoelastic+stress+analysis%5BTitle%5D)+AND+%22Compos+Sci+Technol%22%5BJournal%5D)">Determination of hygrothermal ageing effects in sandwich construction joints using thermoelastic stress analysis.</a> Compos Sci Technol. 63, 211-223 (2003).</li>
<li>Jeon, J., Muliana, A., La Saponara, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Thermal+stress+and+deformation+analyses+in+fiber+reinforced+polymer+composites+undergoing+heat+conduction+and+mechanical+loading%5BTitle%5D)+AND+%22Compos.+Struct%22%5BJournal%5D)">Thermal stress and deformation analyses in fiber reinforced polymer composites undergoing heat conduction and mechanical loading.</a> Compos. Struct. 111, 31-44 (2014).</li>
<li>Muliana, A. H., Rajagopal, K. R., Wineman, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+new+class+of+quasi-linear+models+for+describing+the+non-linear+viscoelastic+response+of+materials%5BTitle%5D)+AND+%22Acta+Mech%22%5BJournal%5D)">A new class of quasi-linear models for describing the non-linear viscoelastic response of materials.</a> Acta Mech. 224, 2169-2183 (2013).</li>
<li>Joshi, N., Muliana, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Deformation+in+Viscoelastic+Sandwich+Composites+Subject+to+Moisture+Diffusion%5BTitle%5D)+AND+%22Compos.+Struct%22%5BJournal%5D)">Deformation in Viscoelastic Sandwich Composites Subject to Moisture Diffusion.</a> Compos. Struct. 92, 254-264 (2010).</li>
<li>Muliana, A. H., Sawant, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Viscoelastic+Responses+of+Polymer+Composites+with+Temperature+and+Time+Dependent+Constituents%5BTitle%5D)+AND+%22Acta+Mech%22%5BJournal%5D)">Viscoelastic Responses of Polymer Composites with Temperature and Time Dependent Constituents.</a> Acta Mech. 204, 155-173 (2009).</li>
<li><a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Standard+Test+Method+for+Moisture+Absorption+Properties+and+Equilibrium+Conditioning+of+Polymer%5BTitle%5D)+AND+%22Matrix+Composite+Materials.+ASTM+International%22%5BJournal%5D)">Standard Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Polymer.</a> Matrix Composite Materials. ASTM International. , (2004).</li>
</ol>

The authors have nothing to disclose.

From the acquired data, it can be seen that the concurrent testing scenario did affect the durability of the closed-cell polyurethane foam specimens. This can be seen by comparing the significantly different displacements (Figure 5) and residual loads to failure (Figure 6) of dry and wet specimens. Figure 7 shows pictures of the specimens after the residual strength tests. It should also be observed that, while the displacement of the dry specimens reached steady state w...

Polymer and fiber-reinforced polymer (FRP) composites have been adopted in a variety of engineering structures, ranging from aircraft and spacecraft, naval vessels, civil infrastructure, (see for examples reviews of Katnam et al.1, Hollaway2, Mouritz et al.3), cars and trains, wind turbine blades, to prosthetics and biomaterials for sutures and implants. These materials&#8217; durability is affected by complex service scenarios, which may include a combination of a) thermo-mechanical loading, e.g., freeze-thaw cycles in civil infrastructure4, subsonic/supersonic flight profiles5, wear in metal-backed polyethylene6); b) degradation due to environmental and chemical agents, e.g., sea water, de-icing, hydraulic fluid for aerospace and naval structures7-10, degradation of polymethylmethacrylate dental composites due to saliva11; c) complex interactions of materials in fastened or bonded joints, e.g., galvanic corrosion and debonding between dissimilar materials, whether in a carbon/fiber patch repair on an aircraft aluminum skin, or a carbon/PEEK bone plate fastened by stainless steel12.
There is unfortunately limited knowledge of the impact of concurrent in-service stimuli on the long-term durability of these materials. Most polymers may be categorized as viscoelastic materials. Mechanical loadings and environmental conditions significantly influence the viscoelastic response of polymers. Hence, reliable models for these materials&#8217; long-term behavior should be able to incorporate time-dependent responses to coupled hygrothermal, mechanical, chemical stimuli. This in turn will improve design predictions, safety and condition-based maintenance/replacement protocols.
There is a large literature body on experimental testing on hygrothermal effects, for example hygrothermal diffusion tests: if the scale of the samples allows it, the material samples may be positioned in a chamber at desired humidity and temperature levels. The samples are removed periodically to measure their mass and/or volume changes for a given amount of time, from weeks to years10,13-17. The hygrothermal test may be followed by mechanical testing, i.e., residual static/fatigue strength/fracture mechanics testing17-19, which only gives information on the effect of hygrothermal stimulus on the mechanical responses of materials. Test data may be fitted to diffusion models of varying complexity, from simple Fickian diffusion to models that include dependency on concentration, stress, temperature, reversible physical aging/plasticization and irreversible chemical reactions. This experimental output may be further incorporated in structural analyses.
Few authors have addressed the impact of simultaneous hygrothermal and mechanical stimuli. Among those researching FRP composites, Neumann and Garom20 immersed stressed and unstressed specimens in distilled water. Stress was applied by positioning the specimens inside compressed stainless steel springs, tuning the load by using different spring stiffnesses and compressive loads. A similar procedure is reported by Wan et al.21. Helbling and Karbhari22 employed a bending fixture inside an environmental chamber for different relative humidity percentages (RH%) and temperature levels. The pre-conditioned specimens were subjected to a given bending strain level, corresponding to a percentage of the static ultimate tensile strain for that composite. Kasturiarachchi and Pritchard23 prepared a stainless steel 4-point bending jig (one per specimen) that was positioned on a shelf in a large glass desiccator. The desiccator was partially filled with distilled water, had small leaks to prevent the buildup of pressure, and was placed in a humidity chamber at 95% RH. Gellert and Turley7 investigated marine-grade FRP composite specimens for their durability under combined creep loading and 100% RH. Their samples were loaded in 4-point bending at a constant load equal to 20% of the failure static flexure load, while fully immersed in sea water. The creep deflection was acquired periodically by using a thickness gauge between the outer surface of the beam in the central cross-section, and a glass plate (it is inferred that such measurement was performed outside the chamber). Abdel-Magid et al.24 placed samples of glass/epoxy in an Invar environmental fixture which was provided by NASA Langley, as the specimens were loaded in tension along the fiber direction, at 20% of the ultimate axial load. Ellyin and Rohrbarcher25 ran hygrothermal tests for up to 140 days, and then tested the specimens in fatigue on a hydraulic testing machine. The specimens were wrapped in a wet cheese cloth connected to a tube and a water supply. Earl et al.26 positioned their loading fixture and the specimens in a large environmental chamber (5.5 m3).
As discussed in many experimental studies, the environmental conditions affect the polymers&#8217; mechanical properties and responses. Some limited experiments also show that the existence of mechanical stress/strain influences the diffusion process in the polymers. Hence, to enhance understanding on the overall performance of polymer-based materials under both mechanical and non-mechanical effects, there is a need for concurrent testing.
There were several objectives behind the design of the testing platform discussed in this paper. First, the platform is part of the experimental setup in a multi-year investigation on the hygrothermo-mechanical behavior of different types of FRP sandwich composites for wind turbine and naval engineering applications. The test data are used to calibrate the parameters in the viscoelastic constitutive equations for the polymeric composites. The constitutive models are based on the work developed over the years by Muliana and collaborators27-30. The second objective was to have a low-cost and user-friendly testing platform, for example one that could be easily relocated in a laboratory (e.g., to a scale for mass measurements, or to the source of the fluid, e.g., one coming from a faucet, a fumehood or a flammable cabinet). The third goal was to create a testing platform that is resistant to a number of chemicals commonly used in service (particularly hydraulic fluid, de-icing, cleaning solvents for aerospace applications8-10), thus specimens could be immersed in such chemicals, and their durability could be assessed.
The chamber (Figure 1) was constructed with high-density polyethylene, which has high chemical resistance. As mentioned above, it is expected that future work will include hygrothermo-mechanical investigation of composites immersed in hydraulic fluid, de-icing, cleaning solvents. Since thermal regulation is an integral aspect of testing, expanded polystyrene foam was fit around the sides of the tank and secured in place by tape and the steel frame itself, to prevent heat exchange with the environment.
The lid of the chamber (Figure 2) was manufactured from transparent, 9.525 mm-thick polycarbonate, allowing the users to observe the specimens during testing without disturbing the test. The lid is secured in place by aluminum T-bars, which were machined to slide under overhanging brackets on the sides of the tank.
Bending in the specimens is enacted by three aluminum blocks, which hang down from the lid, and are fastened through slots in the lid. The three blocks allow up to four specimens to be tested at one time, while the lid slots allow the block spacing to be adjusted depending on the length of the specimens. Each block is rounded at the contact edge to a 12.7 mm diameter, in adherence to ASTM standard D790-10. The specimens are positioned beneath two of the three blocks, with an upward force applied at its center to induce bending (Figures 1-2).
The apparatus was designed with maximum versatility and ease-of-use in mind. Casters with 41.275 mm diameter are fastened beneath the chamber for mobility purposes. Above them, the tank is supported by a welded steel frame with a wire mesh bottom and cross beams for support. Angle stock spacers for the outside tank corners were manufactured to keep the insulation from being crushed by the overhead weight and displacement gauges (string pot apparatus, discussed later). Around the top, angle stock was used again for framing. Pulley and string potentiometer systems to measure mid-span deflection are mounted on four steel, square-tubing arches (Figure 3). The center two arches out of these four carry the string potentiometers and are adjustable to account for specimen versatility. The string potentiometers were constructed using a torsional spring (as can be found in retractable key lanyards) and potentiometers with three-pronged electronic outputs. The pulleys are aligned and mounted for use with a steel cable running from a rigid connection by the specimen to a hanging rod over the side of the chamber for adjustable weight application.
The load is applied to the specimen using a series of cables, pulleys, linkages and bolts. First, the specimen is placed into the U-bolt so that the 10 mm cross bar is contacting the middle of the span. A 9.525 mm diameter steel rod with eye bolts at each end is then connected to the U-bolt. This steel connection passes through the lid of the chamber. A steel cable and Kevlar thread are attached to the eyebolt opposite the U-bolt. This allows the Kevlar thread from the string potentiometer to read data from a rigid point. The steel cable continues upwards and passes over two pulleys that allow the load to be applied at the periphery of the tank. The cable is then attached to a 9.525 mm diameter steel rod that serves as a slotted weight hanger. This hanger provides a place where the slotted weights can be set in order to apply the desired load.

<table><tbody><tr><td>Aluminum 6061 rectangular bars</td><td>McMaster-Carr, USA</td><td>8975K268, 1668T72, 7062T17,&amp;nbsp;</td><td>Part of testing platform</td></tr><tr><td>Aluminum 6061 90&amp;deg; angles</td><td>McMaster-Carr, USA</td><td>8982K91, 8982K14&amp;nbsp;</td><td>Part of testing platform</td></tr><tr><td>440C stainless steel</td><td>McMaster-Carr, USA</td><td>6253K52</td><td>Part of testing platform</td></tr><tr><td>High-density polyethylene sheets</td><td>Tap Plastics, USA</td><td>N/A (0.236 in. thick x 10.75 in. wide x 16.75 in. long)</td><td>Part of testing platform</td></tr><tr><td>High-density polyethylene sheets</td><td>Tap Plastics, USA</td><td>N/A (0.354 in. thick x 6 in. wide x 10 in. long)</td><td>Part of testing platform</td></tr><tr><td>High-density polyethylene sheets</td><td>Tap Plastics, USA</td><td>N/A (0.354 in. thick x 6 in. wide x 16.75 in. long)</td><td>Part of testing platform</td></tr><tr><td>Polycarbonate sheets</td><td>Tap Plastics, USA</td><td>N/A (0.375 in thick, 11.5 in. wide, 17.5 in long)</td><td>Part of testing platform</td></tr><tr><td>Expanded polystyrene foam</td><td>Home Depot</td><td>Model # 310880 Internet # 202532855</td><td>Part of testing platform</td></tr><tr><td>Galvanized steel rope</td><td>McMaster-Carr, USA</td><td>3498T63</td><td>Part of testing platform</td></tr><tr><td>Steel eye bolt</td><td>McMaster-Carr, USA</td><td>3013T341</td><td>Part of testing platform</td></tr><tr><td>Low-carbon steel 90&amp;deg; angle</td><td>McMaster-Carr, USA</td><td>9017K444&amp;nbsp;</td><td>Part of testing platform</td></tr><tr><td>Low-carbon steel rods</td><td>McMaster-Carr, USA</td><td>8920K84, 8920K75, 8920K231, 8920K135, 8920K84&amp;nbsp;&amp;nbsp;&amp;nbsp;</td><td>Part of testing platform</td></tr><tr><td>Low-carbon steel tubes</td><td>McMaster-Carr, USA</td><td>6527K314, 8910K394, 8910K395, 8920K94&amp;nbsp;&amp;nbsp;</td><td>Part of testing platform</td></tr><tr><td>304 stainless steel U-bolt</td><td>McMaster-Carr, USA</td><td>8896T104</td><td>Part of testing platform</td></tr><tr><td>Steel pulley</td><td>McMaster-Carr, USA</td><td>3099T34</td><td>Part of testing platform</td></tr><tr><td>1008 carbon steel sheets</td><td>McMaster-Carr, USA</td><td>9302T113</td><td>Part of testing platform</td></tr><tr><td>Light duty swivel casters</td><td>Harbor Freight, USA</td><td>41519</td><td>Part of testing platform</td></tr><tr><td>100-lbf Vinyl Weight Set</td><td>Overstock.com</td><td>11767059</td><td>Part of testing platform</td></tr><tr><td>Closed-cell polyurethane foam</td><td>General Plastics, USA</td><td>FR-3704</td><td>Testing samples</td></tr><tr><td>Deionized water</td><td>Faucet, PurLab filtering system</td><td>N/A</td><td>Conditioning fluid of tank</td></tr><tr><td>Torsional spring</td><td>Retractable Key Clip, Ebay, USA</td><td>Lot 10</td><td>Used to build string potentiometer</td></tr><tr><td>Kevlar thread</td><td>Cabela&amp;rsquo;s</td><td>IK-321909</td><td>Used to build string potentiometer</td></tr><tr><td>10 kOhm potentiometer</td><td>Ebay, USA</td><td>3590S-2-103L</td><td>Used to build string potentiometer</td></tr><tr><td>Digital multimeter</td><td>Harbor Freight, USA</td><td>98674</td><td>Used to take resistance measurements of string potentiometer</td></tr></tbody></table>

a testing platform for durability studies of polymers and fiber-reinforced polymer composites under concurrent hygrothermo-mechanical stimuli

A Testing Platform for Durability Studies of Polymers and Fiber-reinforced Polymer Composites under Concurrent Hygrothermo-mechanical Stimuli

The durability of polymers and fiber-reinforced polymer composites under service condition is a critical aspect to be addressed for their robust designs and condition-based maintenance. These materials are adopted in a wide range of engineering applications, from aircraft and ship structures, to bridges, wind turbine blades, biomaterials and biomedical implants. Polymers are viscoelastic materials, and their response may be highly nonlinear and thus make it challenging to predict and monitor their in-service performance. The laboratory-scale testing platform presented herein assists the investigation of the influence of concurrent mechanical loadings and environmental conditions on these materials. The platform was designed to be low-cost and user-friendly. Its chemically resistant materials make the platform adaptable to studies of chemical degradation due to in-service exposure to fluids. An example of experiment was conducted at RT on closed-cell polyurethane foam samples loaded with a weight corresponding to ~50% of their ultimate static and dry load. Results show that the testing apparatus is appropriate for these studies. Results also highlight the larger vulnerability of the polymer under concurrent loading, based on the higher mid-point displacements and lower residual failure loads. Recommendations are made for additional improvements to the testing apparatus.

The testing apparatus has successfully held specimens immersed in a fluid under three-point bending. With reasonable precisions, specimens can be loaded and tested with accurate readouts from the potentiometers for mid-point deflection changes. The change in electrical resistance can be recorded to 4 significant figures, resulting in a displacement resolution of the order of 0.1 µm.
Hygrothermo-mechanical tests were conducted at RT on two groups of four specimens of closed-cell polyurethane fo...

The durability of polymers and fiber-reinforced polymer composites in service is a critical aspect for their designs and condition-based maintenance. We present a novel low-cost laboratory testing platform for the investigation of the influence of concurrent mechanical and environmental loadings, and may help design more efficient yet safer composite structures.

The durability of polymers and fiber-reinforced polymer composites under service condition is a critical aspect to be addressed for their robust designs ...

The overall goal of this procedure is to improve the design and safety of polymer and polymer composites under complex loading conditions. Through the study of their durability under concurrent hydrothermal and mechanical loads, using a low cost flexible user-friendly testing platform. First, polymer composite specimens are positioned into a testing tank.Next, a constant three point bending load is applied, and the specimen is concurrently immersed in fluid with creep loading. The measured resistance readings are converted into displacement changes. For analysis, the weights of the specimens are measured after the concurrent tests.Lastly, the specimens are tested for their residual strength. Thus, the mechanical and design purposes of materials are better understood based on their response to the concurrent loading. The main advantage of this platform over existing methods is that it is low cost, user-friendly, portable, and easily adaptable to other testing needs.The applications of this work stands towards safer engineering structures made of polymers and polymer composites, such as aircraft, ships, bridges, and wind turbines. We will have better understanding and therefore better numerical models and designs of these structures under complex service conditions. We're currently using this method in order to provide insight into the durability of polymers and polymer composites, immersed in water and under mechanical load.However, it can also be applied to other situations such as the durability of other materials that are routinely subjected to harsh chemicals during service. Generally, individuals new to this platform should pay attention to carefully positioning and loading the samples. The chamber of the testing apparatus is constructed of high density polyethylene, which will robustly tolerate a wide range of temperatures and fluids.Polystyrene foam surrounding the testing tank prevents heat exchange with the environment. The lid of the chamber is 9.5 millimeter thick polycarbonate, which allows for viewing of the loaded specimens. It is secured by aluminum T-bar, which are in turn secured to the tank to accommodate a heavy load.A reinforcing steel frame and additional hooks on the lid are applied. Heavier weights are most often used for residual strength tests. This chamber can apply up to 50 kilograms to each specimen to ensure that the fail point is found.Hanging down from the lid are three aluminum blocks designed to A STM standards. These blocks allow up to four specimens to be tested simultaneously and are adjustable through slots in the chamber lid. The specimens are positioned beneath two of the blocks and an upward force at the center of a block induces bending forces on the specimen.The apparatus has mobile casters at its base and is solidly held together by a steel frame with cross beams and meshing for support. Angled spacers keep the insulation from being crushed by the overhead weight and displacement gauges on the frame pulley and string potentiometer systems measure the mid-span deflections. These potentiometers are constructed of torsional springs.The pulley connect steel cable from a connection by the specimen to a hanging rod for adjustable weight application. The total load applied to the specimen comes from this series of cables, pulley linkages, and bolts. These are explained in the following sections, covering the use of the apparatus to load a specimen into the testing apparatus.First, open the lid of the tank and set the lid onto the side supports. Then load the specimen into the U-bolt. The crossbar must be at the center of the specimen.Now rest the ends of the specimen on the aluminum support. There should be about five to 10 millimeters of overhang. Continue loading up to four specimens in the same manner.Then remove the lid supports and lower the lid. Make certain that the lid is correctly seated on the tank. Now, apply the desired force to the specimens by adding weights to the steel rod hanging from the outer pulley.First, make sure the potentiometer line is tight. Then measure the resistance across the outer pins of the potentiometer. The black lead goes to pin one and the red lead goes to pin three.Now, convert the resistance reading into displacement by computing the calibration factor. In this case, one kilo ohm corresponds to 64.895 millimeters of displacement. For continuous data acquisition, it is possible to connect the string potentiometers to the digital multimeter.After calculating displacement, prepare to weigh the specimens, remove the weights, and the lid of the tank. The specimens can then be transferred to the holding chamber. First, prepare an interim holding chamber for all the specimens with room temperature, testing fluid of the appropriate testing standard.Now to weigh a specimen first, dry it off with a microfiber cloth. Then place it on a high precision scale and record the data reading. If the specimens need to be tested for residual strength, proceed with those tests.High growth thermal mechanical tests were conducted at room temperature on two groups of four specimens of closed cell polyurethane foam. One group was tested dry at 50%relative humidity. The second group was tested wet in deionized water.Mid-span deflection was tracked for the first six hours and later the next day. The wet specimens displacement was substantially greater than the dry specimens. The residual strength of the specimens was tested by loading until failure.The wet specimens failed at about three kilograms, and the dry specimens failed at about 3.6 kilograms. If the setup is performed properly, the specimens can be positioned and loaded in this platform in 15 minutes. While following this procedure, it's important to remember to position and load the samples properly, especially if they require a significant weight for the durability study Following this procedure.Other studies such as the durability of composites and harsh service chemicals can be performed in order to answer additional questions on the durability of these materials. After watching this video, you should have a good understanding of how to test polymers and polymer composites using these low cost user-friendly testing setup. If working with harsh chemicals, remember to adhere to the precautions indicated in the material safety sheets and environmental health and safety.

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Research

JoVE Journal

Engineering

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Learn a low-cost testing method for polymer composite durability under concurrent hydrothermal and mechanical loads using a flexible platform. This approach improves material design and safety for engineering structures.

A Testing Platform for Durability Studies of Polymers and Fiber-reinforced Polymer Composites under Concurrent Hygrothermo-mechanical Stimuli (Video) | JoVE Journal

A Testing Platform for Durability Studies of Polymers and Fiber-reinforced Polymer Composites under Concurrent Hygrothermo-mechanical Stimuli

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