The publication of this work was supported by the Faculty of Civil and Environmental Engineering at Gdansk University of Technology.

1. Accelerated thermal ageing experiments on technical fabric
<ol>
	<li>Overall preparation
	<ol>
		<li>Prepare a testing machine with proper software (in order to provide constant strain rate tests) and a video extensometer.</li>
		<li>Prepare a thermal chamber providing constant temperature of 80 &#176;C (&#177; 1 &#176;C) and 90 &#176;C (&#177;1 &#176;C) for at least 12 weeks.</li>
	</ol>
	</li>
	<li>Specimen preparation
	<ol>
		<li>Unroll the technical fabric AF9032 bale. Draw the desired shapes (300 mm x 50 mm) with a soft pencil or marker on the fabric surface parallel to the warp or fill direction. 
		NOTE: The distribution of specimens on the fabric surface is given elsewhere17.</li>
		<li>Indicate the warp direction on each specimen with a permanent marker. Cut the specimens with a sharp knife or scissors. Use the ruler if a knife is used for cutting. 
		NOTE: The specimens should be rectangular17. The major load-caring elements of the fabric are threads. In the operational phase, the coating material usually exceeds its yield limit, thus not taking part in the stress distribution. The only elements to carry the load are threads spreading from one grip to another. Therefore, it is not reasonable to use sophisticated shapes of specimens (e.g., a dumbbell shape usually used for metals). On the other hand, such sample shapes result in the need for special grips when the ultimate load is investigated, or the use of an extensometer in order to assess material parameters.</li>
		<li>Measure the specimen&#39;s thickness with a slide caliper and count the number of threads at the short edge of the specimen. 
		NOTE: For each specimen, take three thickness measurements, and compute the average value. Use the magnifying glass to assess the number of threads if necessary.</li>
	</ol>
	</li>
	<li>Turn on the thermal chamber, leaving the door open. Using the buttons and the control display, select the temperature (80 &#176;C). Close the thermal chamber door and observe the increase of temperature on the control panel.</li>
	<li>Specimen warming
	<ol>
		<li>When the temperature is close to 80 &#176;C, open the thermal chamber door. Insert at least 7 sets of specimens with each set consisting of 6 specimens cut in the warp direction and 6 in the fill direction. Close the door as soon as possible in order to avoid a temperature drop. 
		NOTE: The experiments should be conducted for three strain rates. For each strain rate, experiments are performed on two specimens in the warp direction and two in the fill direction. Place excess specimens in the chamber in case the experiments are not successful or the results from both tests are highly divergent.</li>
		<li>After 1 h, don thermal gloves and remove the first set of specimens (the reference set; 6 specimens in the warp direction and 6 in the fill direction). After every 2 weeks, remove a succeeding set of specimens from the thermal chamber. 
		NOTE: The entire warming process will take 12 weeks.</li>
	</ol>
	</li>
	<li>Specimen conditioning
	<ol>
		<li>Leave the specimens at room temperature for one week. Cool the specimens to room temperature (i.e., their properties should be stabilized).</li>
		<li>Before the test, draw two black marks (dots) using a permanent marker with a lengthwise separation of about 50 mm (L0) in the middle of each specimen. 
		NOTE: The dots will be used by the video extensometer.</li>
	</ol>
	</li>
	<li>Testing machine setup
	<ol>
		<li>Install four 60 mm flat inserts into the testing machine, two inserts per one grip. The inserts show a fish scale surface type and are used to avoid slipping the specimens out of the grips.</li>
		<li>Switch on the machine. Start the software (e.g., TestXpert) that controls the machine. Choose the program dedicated to the tensile tests.</li>
		<li>Select the starting position with a 200 mm grip to grip separation in the software. Click the Starting Position button to execute the 200 mm grip to grip separation. This grip position is usually called the starting position for a test. 
		NOTE: The 200 mm distance is required by the ISO standard17.</li>
	</ol>
	</li>
	<li>Video extensometer setup
	<ol>
		<li>Move the camera of the video extensometer along the supporting bar to situate the lens of the camera at the level of the middle part of the specimen. Check whether the lens of the camera provides a clear view of the specimen markers during the whole experiment. 
		NOTE: Perform a similar test before the main test to establish the probable sample elongation range to ensure that the camera will follow the black markers during an entire test.</li>
		<li>Select the proper brightness and focus for the lens using the computer screen and the associated software.</li>
	</ol>
	</li>
	<li>Video extensometer calibration 
	NOTE: The calibration device is the standard equipment of the video extensometer.
	<ol>
		<li>Put the calibration device in the front of the camera and clamp it with the grips.</li>
		<li>Using the video extensometer software (e.g., VideoXtens), select the proper type of markers in the Targets window (usually black and white).</li>
		<li>Select the calibration procedure in the video extensometer software using the Scale option and choose the calibration distance in the Scale window. 
		NOTE: The distance should be similar to the separation of markers on the specimens. The calibration device offers three measuring distances: 10, 15 and 40 mm. Due to the 50 mm marker separation, the 40 mm distance is appropriate.</li>
		<li>After calibration, change the marker type to Pattern in the Targets window. 
		NOTE: This enables the video extensometer to follow the markers indicated on the specimen.</li>
	</ol>
	</li>
	<li>Test performance
	<ol>
		<li>Prepare the test parameters in the TextXpert software. 
		NOTE: The prepared program must enable a test with a selected strain rate in the uniaxial stress case. It must be correlated with the video extensometer. The recorded parameters are the initial distance of the extensometer markers (L0), and result functions of time, grip displacements, current extensometer&#39;s markers distance, and force. The pre-load force of 50 N17 is programmed and the L0 distance is adjusted after preloading.</li>
		<li>Put the specimen along the machine main vertical axis and close the grips using the tubular spanner. 
		NOTE: The specimen must be located symmetrically to the grips in the vertical and horizontal directions.</li>
		<li>Perform the tests with the selected constant strain rate until the specimens break (use 0.005, 0.001, and 0.0001 s-1 strain rates). For each strain rate, test at least two specimens in the warp direction and fill direction. Save the test results. 
		NOTE: The following data are necessary: the initial distance of the extensometer markers (L0), time functions of the extensometer&#39;s marker distance, and the force.</li>
	</ol>
	</li>
	<li>Repeat steps 1.5&#8722;1.9 every two weeks using the other sets of samples (six times, up to 12 weeks).</li>
	<li>Repeat the entire procedure at 90 &#176;C. The total number of specimens does not change. The ageing process lasts 6 weeks. Remove and test subsequent sets of specimens every week.</li>
</ol>
2. Data preparation
<ol>
	<li>Knowing the cross section area of the samples, use graphing software (SigmaPlot18 or similar) to recalculate the registered force and elongation increments according to elementary strength of material equations to the stress-strain relations. Plot a graph of obtained data, separately, for the warp and fill samples and for each of the strain rates.</li>
	<li>Repeat for the 80 &#176;C and 90 &#176;C results.</li>
</ol>
3. Parameter identification of material models
<ol>
	<li>Piecewise linear model for non-linear elastic modeling 
	NOTE: The application of the piecewise linear material model is possible when the stress-strain curve can be split into sections of linear (or approximately linear) shapes. Particular crossing points of the lines at neighboring sections correspond to applicability ranges of the related lines19.
	<ol>
		<li>In the case of every curve obtained in step 2.1, find the strain ranges, detecting the linear or close to linear stress-strain relation.</li>
		<li>Using the fit regression option in the graphing software and the least square method, identify the best-fit line in the chosen region. 
		NOTE: The tangent to this curve corresponds to the stiffness of the material in a particular range.</li>
		<li>Denote the tangent as Eij where the index i corresponds to the current direction of the material (W for the warp direction and F for the fill direction) and the index j is a consecutive number of the identified line.</li>
		<li>Having parameters of all the lines, find the intersection points between the lines; denote them as &#949;k/l, where k and l mark the crossing lines. 
		NOTE: These points (&#949;k/l) constitute the strain ranges to apply the particular longitudinal stiffness values (Eij) (Figure 1).</li>
	</ol>
	</li>
	<li>Bodner&#8211;Partom viscoplastic model 
	NOTE: The Bodner&#8211;Partom constitutive law is used to reflect the elasto-viscoplastic behavior of various materials20,21. The basics and mathematical formulation of the model is given in detail elsewhere20,21,22,23,24,25. The elementary equations are presented in Table 1 only to model the uniaxial stress state. The Bodner&#8211;Partom model parameters are identified by means of the uniaxial tensile tests conducted with at least three different strain rates. The value of the strain rate must be constant at least in the inelastic part of the experiment. The complete Bodner&#8211;Partom model identification procedure modified for technical woven fabrics is widely presented24,25.
	<ol>
		<li>Using the graphing software, identify Bodner&#8211;Partom model parameters following Klosowski et al.24.</li>
	</ol>
	</li>
</ol>
4. Arrhenius extrapolation
NOTE: The Arrhenius law is based on an empirical observation that ambient temperature increase results in acceleration of a number of chemical reactions that may speed up the ageing process as well. The complete mathematical representation of the Arrhenius chemical reaction concept can be found elsewhere11,26. The Arrhenius law in a simplified form is called &#34;the 10 degree rule&#34;27. According to this rule, a surrounding temperature increase of about 10 &#176;C theoretically doubles the rate of the aging process. Hence, the reaction rate f is defined as follows17:
<img alt="Equation 1" src="/files/ftp_upload/60737/60737equ07.jpg" />
where &#916;T = T - Tref is the difference between the ageing temperature T and the service temperature Tref of a material.
<ol>
	<li>Assume the temperature Tref according to the average value based on the results of the local meteorological station (here, Tref = 8 &#176;C28). Assume the thermal chamber temperature T to be used in the ageing test (here, 80 &#176;C and 90 &#176;C). 
	NOTE: The temperature level should be registered for a longer time period, at least one year, and then calculated as the mean value of that period, bringing a time average of this period taken as Tref.</li>
	<li>Calculate the reaction rate constant f from equation 1 and then extrapolate the ageing time (expressed in weeks) to years (Table 2). 
	NOTE: The extrapolation effects of different ageing time periods conducted within the current research are presented in Table 3. For instance, thermal ageing of a specimen in 4 weeks at 90 &#176;C is equal to its ageing in 8 weeks at 80 &#176;C and corresponds to a natural ageing of approximately 23 years.</li>
</ol>
5. Data representation
<ol>
	<li>Present the obtained parameter values in the normalized form of X/X0, where X denotes a current value of the certain parameter and X0 corresponds to the initial value of this parameter, with regard to a specimen aged 1 hour only. 
	NOTE: The time of artificial thermal ageing is set up in hours.</li>
	<li>Plot X/X0 values on the Y axis versus the ageing time plotted on the X axis to show the evolution of the parameters. Prepare plots for the warp and fill directions of the tested material separately.</li>
	<li>Describe the parameter values plotted over time by linear functions (or different best-fit functions) using the least square method and report R2 values.</li>
	<li>To evaluate whether the Arrhenius simplified relation is correct for AF9032 fabric, redraw the results obtained for 90 &#176;C with respect to the ageing time recalculated into &#34;real&#34; time according to the Arrhenius law.</li>
</ol>

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The authors have nothing to disclose.

This article incudes a detailed experimental protocol to simulate the laboratory accelerated experiments on polyester reinforced and PVC coated fabrics for civil engineering applications. The protocol describes the case of artificial thermal ageing only by the means of raising the ambient temperature. This is an obvious simplification of real weather conditions, as UV radiation and water influence play an additional role in material service ageing.
Generally, the conditions of accelerated agei...

Polyester based architectural fabrics are commonly used for construction of hanging roofs1. Being relatively cheap with good mechanical properties, they can be employed in long-term exploitation (e.g., the hanging roof of the Forest Opera in Sopot - Poland). Unfortunately, weather conditions, ultraviolet radiation, biological reasons, and operational purposes (season pre-stressing and loosening2) can affect their mechanical properties. Hanging roofs made of AF9032 are typically seasonal structures subjected to high temperature (especially during sunny days in the summer), regular pre-tensioning and loosening. In order to properly design a hanging roof, fabric parameters must be determined not only at the beginning of exploitation, but also after several years of use.
Ageing analysis measures the ageing indicator and compares the initial and final values of the parameters to assess the impact of ageing. Cash et al.3 proposed one of the simplest methods by comparative analysis of 12 different types of roofing membranes. These membranes were exposed to outdoor weathering for 2 or 4 years. The authors used a rating system of several properties to assess fabric durability. In order to provide an analysis of polymer thermal ageing, the time-temperature superposition principle (TTSP) can be applied4. This principle states that the behavior of a material at low temperature and under low strain level resembles its behavior at high temperature and high strain level. The simple multiplicative factor can be used to relate the current temperature properties with the properties at the reference temperature. Graphically, it corresponds to the curve shift on the log time scale. Regarding the temperature, two methods are proposed to combine the shift factor and the ageing temperature: the Williams-Landel-Ferry (WLF) equations, and the Arrhenius law. Both methods are included in the Swedish standard ISO 113465 to estimate the lifetime and maximum operational temperature for rubber, or vulcanized and thermoplastic, materials. Recently, thermal ageing and Arrhenius methodology have been used in the cable lifetime prediction6,7, heating pipes8, and polymer glue PMMA4. An extension of the Arrhenius law is the Eyring law that takes into account other ageing factors (e.g., voltage, pressure, etc.)9. Alternatively, other studies propose and verify simple linear models for a description of ageing (e.g., biosensor ageing10). Although the Arrhenius method is commonly used, there is discussion on its relevance in the lifetime prediction of every material. Hence, the method must be used with care, especially in terms of initial assumptions and experimental conditions6.
Similar to most polymers, the polyester fabrics used in the current research exhibit two distinct transition phases defined by the melting temperature (Tm) and the glass transition temperature (Tg). The melting temperature (Tm) is the temperature when a material changes from its solid state to the liquid one, and the glass transition temperature (Tg) is the boundary between the glass and rubber states11. According to manufacturer&#39;s data, the AF9032 fabric is made from polyester threads (Tg = 100&#8722;180 &#176;C12, Tm = 250&#8722;290 &#176;C13) and PVC coating (Tg = 80&#8722;87 &#176;C14,15, Tm = 160&#8722;260 &#176;C16). The ageing temperature T&#945; should be selected below Tg. During sunny days, the temperature on the top surface of a hanging roof may even reach 90 &#176;C; thus, two ageing temperatures (80 &#176;C and 90 &#176;C) are tested here. These temperatures are below the thread Tg and close to the coating Tg.
The performance of the accelerated ageing protocol on technical fabrics is presented in the current work. Artificial thermal ageing is used to predict changes of the material properties. The article illustrates appropriate laboratory testing routines and a way to extrapolate relatively short-term experimental results.

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	<tbody>
		<tr>
			<td>AF 9032 technical fabric</td>
			<td>Shelter-Rite Seaman Corporation</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>knife of scisors</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>marker</td>
			<td></td>
			<td></td>
			<td>pernament</td>
		</tr>
		<tr>
			<td>ruler</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Sigma Plot</td>
			<td>Systat Software Inc.</td>
			<td>v. 12.5</td>
			<td></td>
		</tr>
		<tr>
			<td>Testing machine Z020</td>
			<td>Zwick Roell</td>
			<td>BT1-FR020TN.A50</td>
			<td></td>
		</tr>
		<tr>
			<td>TestXpert II program</td>
			<td>Zwick Roell</td>
			<td>v. 3.50</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermal chamber</td>
			<td>Eurotherm Controls</td>
			<td>2408</td>
			<td></td>
		</tr>
		<tr>
			<td>tubular spanner</td>
			<td></td>
			<td></td>
			<td>13 mm</td>
		</tr>
		<tr>
			<td>Video extensometer</td>
			<td>Zwick Roell</td>
			<td>BTC-EXVIDEO.PAC.3.2.EN</td>
			<td>Instead of video extensometer, a mechanical one can be used</td>
		</tr>
		<tr>
			<td>VideoXtens</td>
			<td>Zwick Roell</td>
			<td>5.28.0.0 SP2</td>
			<td></td>
		</tr>
	</tbody>
</table>

artificial thermal ageing of polyester reinforced and polyvinyl chloride coated technical fabric

Architectural fabric AF9032 has been subjected to artificial thermal ageing to determine changes of the material parameters of the fabric. The proposed method is based on the accelerated ageing approach proposed by Arrhenius. 300 mm x 50 mm samples were cut in the warp and fill directions and placed in a thermal chamber at 80 &#176;C for up to 12 weeks or at 90 &#176;C for up to 6 weeks. Then after one week of conditioning at ambient temperature, the samples were uniaxially tensioned at a constant strain rate. Experimentally, the parameters were determined for the non-linear elastic (linear piecewise) and viscoplastic (Bodner&#8211;Partom) models. Changes in these parameters were studied with respect to the ageing temperature and ageing period. In both cases, the linear approximation function was successfully applied using the simplified methodology of Arrhenius. A correlation was obtained for the fill direction between experimental results and the results from the Arrhenius approach. For the warp direction, the extrapolation results exhibited some differences. Increasing and decreasing tendencies have been observed at both temperatures. The Arrhenius law was confirmed by the experimental results only for the fill direction. The proposed method makes it possible to predict real fabric behavior during long term exploitation, which is a critical issue in the design process.

Figure 2 juxtaposes the stress-strain curves for the warp and fill directions of AF9032 fabric obtained at different ageing times, in the 80 &#176;C temperature level for a strain rate of 0.001 s-1. The difference between the 1 h ageing period (reference test) and the rest of the ageing periods is clear. The ageing time does not seem to substantially affect the material response in the warp direction, as the stress&#8211;strain curves are highly repetitive, showing no important di...

Watch this Scientific Journal Video about Artificial Thermal Ageing of Polyester Reinforced and Polyvinyl Chloride Coated Technical Fabric at JoVE.com

Artificial Thermal Ageing of Polyester Reinforced and Polyvinyl Chloride Coated Technical Fabric

Here, we simulate accelerated thermal ageing of technical fabric and see how this ageing process influences the mechanical properties of the fabric.

Architectural fabric AF9032 has been subjected to artificial thermal ageing to determine changes of the material parameters of the fabric. The proposed ...

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6.5K Views.  Gdansk University of Technology. Here, we simulate accelerated thermal ageing of technical fabric and see how this ageing process influences the mechanical properties of the fabric.

Video: Artificial Thermal Ageing of Polyester Reinforced and Polyvinyl Chloride Coated Technical Fabric

The Preparation of Electrohydrodynamic Bridges from Polar Dielectric Liquids

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and polar dielectric liquids. These bridges are unique from capillary bridges in that they exhibit extensibility beyond a few millimeters, have complex bi-directional mass transfer patterns, and emit non-Planck infrared radiation. A number of common solvents can form such bridges as well as low conductivity solutions and colloidal suspensions. The macroscopic behavior is governed by electrohydrodynamics and provides a means of studying fluid flow phenomena without the presence of rigid walls. Prior to the onset of a liquid bridge several important phenomena can be observed including advancing meniscus height (electrowetting), bulk fluid circulation (the Sumoto effect), and the ejection of charged droplets (electrospray). The interaction between surface, polarization, and displacement forces can be directly examined by varying applied voltage and bridge length. The electric field, assisted by gravity, stabilizes the liquid bridge against Rayleigh-Plateau instabilities. Construction of basic apparatus for both vertical and horizontal orientation along with operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

Horizontal and vertical electrohydrodynamic liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields and polar dielectric liquids. The construction of basic apparatus and operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and ...

The Evolution of Silica Nanoparticle-polyester Coatings on Surfaces Exposed to Sunlight

Corrosion of metallic surfaces is prevalent in the environment and is of great concern in many areas, including the military, transport, aviation, building and food industries, amongst others. Polyester and coatings containing both polyester and silica nanoparticles (SiO2NPs) have been widely used to protect steel substrata from corrosion. In this study, we utilized X-ray photoelectron spectroscopy, attenuated total reflection infrared micro-spectroscopy, water contact angle measurements, optical profiling and atomic force microscopy to provide an insight into how exposure to sunlight can cause changes in the micro- and nanoscale integrity of the coatings. No significant change in surface micro-topography was detected using optical profilometry, however, statistically significant nanoscale changes to the surface were detected using atomic force microscopy. Analysis of the X-ray photoelectron spectroscopy and attenuated total reflection infrared micro-spectroscopy data revealed that degradation of the ester groups had occurred through exposure to ultraviolet light to form COO&#903;, -H2C&#903;, -O&#903;, -CO&#903; radicals. During the degradation process, CO and CO2 were also produced.

Two types of surfaces, polyester-coated steel and polyester coated with a layer of silica nanoparticles, were studied. Both surfaces were exposed to sunlight, which was found to cause substantial changes in the chemistry and nanoscale topography of the surface.

Corrosion of metallic surfaces is prevalent in the environment and is of great concern in many areas, including the military, transport, aviation, ...

Strain Sensing Based on Multiscale Composite Materials Reinforced with Graphene Nanoplatelets

The electrical response of NH2-functionalized graphene nanoplatelets composite materials under strain was studied. Two different manufacturing methods are proposed to create the electrical network in this work: (a) the incorporation of the nanoplatelets into the epoxy matrix and (b) the coating of the glass fabric with a sizing filled with the same nanoplatelets. Both types of multiscale composite materials, with an in-plane electrical conductivity of ~10-3 S/m, showed an exponential growth of the electrical resistance as the strain increases due to distancing between adjacent functionalized graphene nanoplatelets and contact loss between overlying ones. The sensitivity of the materials analyzed during this research, using the described procedures, has been shown to be higher than commercially available strain gauges. The proposed procedures for self-sensing of the structural composite material would facilitate the structural health monitoring of components in difficult to access emplacements such as offshore wind power farms. Although the sensitivity of the multiscale composite materials was considerably higher than the sensitivity of metallic foils used as strain gauges, the value reached with NH2 functionalized graphene nanoplatelets coated fabrics was nearly an order of magnitude superior. This result elucidated their potential to be used as smart fabrics to monitor human movements such as bending of fingers or knees. By using the proposed method, the smart fabric could immediately detect the bending and recover instantly. This fact permits precise monitoring of the time of bending as well as the degree of bending.

The integration of conductive nanoparticles, such as graphene nanoplatelets, into glass fiber composite materials creates an intrinsic electrical network susceptible to strain. Here, different methods to obtain strain sensors based on the addition of graphene nanoplatelets into the epoxy matrix or as a coating on glass fabrics are proposed.

The electrical response of NH2-functionalized graphene nanoplatelets composite materials under strain was studied. Two different manufacturing methods are ...

Inkjet-printed Polyvinyl Alcohol Multilayers

Inkjet printing is a modern method for polymer processing, and in this work, we demonstrate that this technology is capable of producing polyvinyl alcohol (PVOH) multilayer structures. A polyvinyl alcohol aqueous solution was formulated. The intrinsic properties of the ink, such as surface tension, viscosity, pH, and time stability, were investigated. The PVOH-based ink was a neutral solution (pH 6.7) with a surface tension of 39.3 mN/m and a viscosity of 7.5 cP. The ink displayed pseudoplastic (non-Newtonian shear thinning) behavior at low shear rates, and overall, it demonstrated good time stability. The wettability of the ink on different substrates was investigated, and glass was identified as the most suitable substrate in this particular case. A proprietary 3D inkjet printer was employed to manufacture polymer multilayer structures. The morphology, surface profile, and thickness uniformity of inkjet-printed multilayers were evaluated via optical microscopy.

An inkjet printer was used to manufacture polyvinyl alcohol multilayers. Polyvinyl alcohol water-based ink was formulated, and the main physical properties were investigated.

Inkjet printing is a modern method for polymer processing, and in this work, we demonstrate that this technology is capable of producing polyvinyl alcohol ...

Experimental Protocol to Determine the Chloride Threshold Value for Corrosion in Samples Taken from Reinforced Concrete Structures

The aging of reinforced concrete infrastructure in developed countries imposes an urgent need for methods to reliably assess the condition of these structures. Corrosion of the embedded reinforcing steel is the most frequent cause for degradation. While it is well known that the ability of a structure to withstand corrosion depends strongly on factors such as the materials used or the age, it is common practice to rely on threshold values stipulated in standards or textbooks. These threshold values for corrosion initiation (Ccrit) are independent of the actual properties of a certain structure, which clearly limits the accuracy of condition assessments and service life predictions. The practice of using tabulated values can be traced to the lack of reliable methods to determine Ccrit on-site and in the laboratory.
Here, an experimental protocol to determine Ccrit for individual engineering structures or structural members is presented. A number of reinforced concrete samples are taken from structures and laboratory corrosion testing is performed. The main advantage of this method is that it ensures real conditions concerning parameters that are well known to greatly influence Ccrit, such as the steel-concrete interface, which cannot be representatively mimicked in laboratory-produced samples. At the same time, the accelerated corrosion test in the laboratory permits the reliable determination of Ccrit prior to corrosion initiation on the tested structure; this is a major advantage over all common condition assessment methods that only permit estimating the conditions for corrosion after initiation, i.e., when the structure is already damaged.
The protocol yields the statistical distribution of Ccrit for the tested structure. This serves as a basis for probabilistic prediction models for the remaining time to corrosion, which is needed for maintenance planning. This method can potentially be used in material testing of civil infrastructures, similar to established methods used for mechanical testing.

We propose a method to measure a parameter that is highly relevant for corrosion assessments or predictions of reinforced concrete structures, with the main advantage of permitting testing of samples from engineering structures. This ensures real conditions at the steel-concrete interface, which are crucial to avoid artifacts of laboratory-made samples.

The aging of reinforced concrete infrastructure in developed countries imposes an urgent need for methods to reliably assess the condition of these ...

Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous light irradiation. The photo-excitation of dopants that can quickly dissipate light into heat, coupled with anisotropic thermal expansion and self-shadowing of the film, gives rise to the self-sustained deformation. The oscillations observed are influenced by the dimensions and the modulus of the film, and by the directionality and intensity of the light. The system developed offers applications in energy conversion and harvesting for soft-robotics and automated systems.
The general method described here consists of creating free-standing liquid crystalline films and characterizing the mechanical and thermal effects observed. The molecular alignment is achieved using alignment layers (rubbed polyimide), commonly used in the display manufacturing industry. To obtain actuators with large deformation, the mesogens are aligned and polymerized in a splay/bend configuration, i.e., with the director of the liquid crystals (LCs) going gradually from planar to homeotropic through the film thickness. Upon irradiation, the mechanical and thermal oscillations obtained are monitored with a high-speed camera. The results are further quantified by image analysis using an image processing program.

The goal of the protocol is to create liquid crystalline polymer films that can mechanically oscillate under continuous light irradiation. We describe in great detail the conception of free-standing films, from the liquid crystal alignment method to the photo-actuation. The experimental protocol applied to prepare this material is broadly applicable.

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous ...

Preparation of Aligned Steel Fiber Reinforced Cementitious Composite and Its Flexural Behavior

The aim of this work is to present an approach, inspired by the way in which a compass needle maintains a consistent orientation under the action of the Earth&#39;s magnetic field, for manufacturing a cementitious composite reinforced with aligned steel fibers. Aligned steel fiber reinforced cementitious composites (ASFRC) were prepared by applying a uniform electromagnetic field to fresh mortar containing short steel fibers, whereby the short steel fibers were driven to rotate in alignment with the magnetic field. The degree of alignment of steel fibers in hardened ASFRC was assessed both by counting steel fibers in fractured cross-sections and by X-ray computed tomography analysis. The results from the two methods show that the steel fibers in ASFRC were highly aligned while the steel fibers in non-magnetically treated composites were randomly distributed. The aligned steel fibers had a much higher reinforcing efficiency, and the composites, therefore, exhibited significantly enhanced flexural strength and toughness. The ASFRC is thus superior to SFRC in that it can withstand greater tensile stress and more effectively resist cracking.

This protocol describes an approach for manufacturing aligned steel fiber reinforced cementitious composite by applying a uniform electromagnetic field. Aligned steel fiber reinforced cementitious composite exhibits superior mechanical properties to ordinary fiber reinforced concrete.

The aim of this work is to present an approach, inspired by the way in which a compass needle maintains a consistent orientation under the action of the ...

Installation Method to Enhance Quality Control for Fiber Reinforced Polymer Spike Anchors

Fiber reinforced polymer (FRP) anchors are a promising way to enhance the performance of externally-bonded FRPs applied to existing structures, as they can delay or even prevent debonding failure. However, a major concern faced by designers is the premature failure of the anchors due to stress concentration. Poor installation quality and preparation of the clearance holes can result in stress concentration that provokes this premature failure. This paper deals with an installation method that aims to reduce the impact of the stress concentration and to provide a proper quality control of the preparation of the drill hole. The method involves three parts: the drilling and cleaning of the holes, the smoothing of the hole edges with a customized drill bit, and the installation of the anchor itself, including the impregnation of the anchor dowel and its insertion. Anchor fans (the free length of the spikes) are then bonded to the external FRP reinforcement. For the end anchorage, and in the case of reinforcements with multiple plies, it is recommended that the anchor fan be inserted between two plies to assist the stress-transfer mechanism. 
The proposed procedure is complemented with a design approach for spike anchors, based on an extensive database. It is proposed that the design follow a number of steps, namely: selection of the anchor diameter and subsequent tensile strength of the connector (that is to say, the anchor before fanning out the free end), evaluation of the reduction in the tensile strength due to bending, provision of enough embedment to prevent slippage failure, and consideration of the number and spacing of anchors for a given reinforcement. In this sense, it should be noted that further research is needed in order to obtain a general expression for the contribution of spike anchors to overall bond strength of FRP reinforcements.

This manuscript presents a method for controlling the quality of installation for spike anchors designed to delay delamination of externally bonded fiber reinforced polymers. The protocol includes the preparation of the drill hole and the insertion process. The most influential parameters on the efficiency of the anchors are discussed.

Fiber reinforced polymer (FRP) anchors are a promising way to enhance the performance of externally-bonded FRPs applied to existing structures, as they ...

Cutting Procedures, Tensile Testing, and Ageing of Flexible Unidirectional Composite Laminates

Many body armor designs incorporate unidirectional (UD) laminates. UD laminates are constructed of thin (&#60;0.05 mm) layers of high-performance yarns, where the yarns in each layer are oriented parallel to each other and held in place using binder resins and thin polymer films. The armor is constructed by stacking the unidirectional layers in different orientations. To date, only very preliminary work has been performed to characterize the ageing of the binder resins used in unidirectional laminates and the effects on their performance. For example, during the development of the conditioning protocol used in the National Institute of Justice Standard-0101.06, UD laminates showed visual signs of delamination and reductions in V50, which is the velocity at which half of the projectiles are expected to perforate the armor, after ageing. A better understanding of the material property changes in UD laminates is necessary to comprehend the long-term performance of armors constructed from these materials. There are no current standards recommended for mechanically interrogating unidirectional (UD) laminate materials. This study explores methods and best practices for accurately testing the mechanical properties of these materials and proposes a new test methodology for these materials. Best practices for ageing these materials are also described.

The goal of the study was to develop protocols to prepare consistent specimens for accurate mechanical testing of high-strength aramid or ultra-high-molar-mass polyethylene-based flexible unidirectional composite laminate materials and to describe protocols for performing artificial ageing on these materials.

Many body armor designs incorporate unidirectional (UD) laminates. UD laminates are constructed of thin (&#60;0.05 mm) layers of high-performance yarns, ...

Fabric Moisture Uniform Control to Study the Influence of Air Impingement Parameters on Fabric Drying Characteristics

Impinging dryness is now a widely used and effective way for fabric drying due to its high heat and mass transfer coefficient. Previous studies on fabric drying have neglected the contributions of moisture uniformity and diffusion coefficient to the drying process; though, they have recently been shown to have a significant influence on drying characteristics. This report outlines a step-by-step procedure to investigate the effects of air impingement parameters on a fabric&#39;s drying characteristics by controlling the uniformity of its area moisture distribution. A hot air blower unit equipped with an angle adjustable nozzle is used to generate air flow with different velocities and temperatures while the drying process is recorded and analyzed using an infrared thermograph. In addition, a uniform padder is adapted to ensure the fabric&#39;s moisture uniformity. Impinging drying is studied under different initial conditions by changing the air flow temperature, velocity, and direction, then the applicability and suitability of the protocol are evaluated.

Presented here is a protocol that guarantees uniform distribution of initial moisture inside of a fabric and investigates the effects of hot-air thermodynamic parameters (velocity, temperature, and direction) and thickness on the fabric&#39;s drying characteristics (e.g., temperature variation) under the condition of air impingement.

Impinging dryness is now a widely used and effective way for fabric drying due to its high heat and mass transfer coefficient. Previous studies on fabric ...