Dynamic Tensile Strain Research Articles

Dynamic tensile properties of flax fiber reinforced polymer composites

Flax fibers have been widely used as reinforcing materials due to the growing demand for the development of sustainable materials. They are cost-effective and have excellent mechanical properties. In this study, the dynamic tensile properties of flax FRP coupons were tested using an Instron VHS high rate testing system. The effect of strain rate on the failure process, failure modes, tensile strength, failure strain, and Young’s modulus of flax FRP coupons were discussed and analyzed within the strain rate less than 164.2 s−1. The failure process at different strain rates were captured by a high-speed camera. It was observed that the specimen failed with only one cross-sectional fracture at a relatively low strain rate. At a relatively high strain rate, more than one fracture was observed. The experimental results indicated that the dynamic tensile strength increased, failure strain decreased, and Young’s modulus remained almost unchanged when the strain rate was less than 41.3 s−1. As it was over 41.3 s−1, the dynamic tensile strength, failure strain, and Young’s modulus had a prominent rise. To describe the dynamic tensile strength, failure strain, and Young’s modulus at a certain strain rate, empirical equations based on the experimental data were proposed for reference.

A Comparative Study on the Dynamic Tensile Strength Evaluation Method of Rock Materials

The representative calculation methods of dynamic tensile strength applied to the spalling test are comparatively reviewed in the same experimental cases. The results are compared with those of the ISRM suggested dynamic BD method. Through comparative verification results and analysis of methodological characteristics of each determination method in the spalling test, the most reasonable method for calculating dynamic tensile strength in the high strain rate condition is derived. The local strain rate and apparent strain rate are calculated for the same experimental cases, and the difference in the result values according to the strain rate calculation technique is analyzed through comparative verification of the calculated results. Consequently, the characteristics of each dynamic tensile strength determination method and strain rate calculation method in the spalling test are presented, and the results of the review on the most suitable method for calculating the dynamic tensile strength of rock materials are presented.

Experimental and numerical research of crack propagation process and energy dissipation law of grouting specimens under radial impact load

Different air pressures are used to conduct an impact test based on the split Hopkinson pressure bar (SHPB) test system to study the crack evolution process and energy dissipation law of the cemented rock under impact load. The failure mechanism of the specimens is analyzed from the perspective of dynamic failure process and energy dissipation. The spatial distribution of the specimen components visualized by the image reconstruction technology and the LS-DYNA mesoscopic model is established. Results show that the proportion of dissipated energy, the dynamic tensile strength and peak strain of the specimens increase with strain rate increase. The crack evolution process of the model is quantitatively described under an impact load, which is divided into four stages, namely, no crack stage, slow development stage, accelerated propagation stage and penetration stage. Compared with the indoor and simulation test result, the crack evolution process and failure modes are consistent under different strain rates. When the specimens are destroyed, the energy dissipation rate fluctuates from 10% to 13%. The dissipated energy of cement paste accounts for more than 90% of the total dissipated energy. The cement paste damages first and its strength has a great influence on the strength of the grouting specimens. This study provides a reference to evaluate the cemented rock under a dynamic load.

A Tale of Two Loads: Modulation of IL-1 Induced Inflammatory Responses of Meniscal Cells in Two Models of Dynamic Physiologic Loading.

Meniscus injuries are highly prevalent, and both meniscus injury and subsequent surgery are linked to the development of post-traumatic osteoarthritis (PTOA). Although the pathogenesis of PTOA remains poorly understood, the inflammatory cytokine IL-1 is elevated in synovial fluid following acute knee injuries and causes degradation of meniscus tissue and inhibits meniscus repair. Dynamic mechanical compression of meniscus tissue improves integrative meniscus repair in the presence of IL-1 and dynamic tensile strain modulates the response of meniscus cells to IL-1. Despite the promising observed effects of physiologic mechanical loading on suppressing inflammatory responses of meniscus cells, there is a lack of knowledge on the global effects of loading on meniscus transcriptomic profiles. In this study, we compared two established models of physiologic mechanical stimulation, dynamic compression of tissue explants and cyclic tensile stretch of isolated meniscus cells, to identify conserved responses to mechanical loading. RNA sequencing was performed on loaded and unloaded meniscus tissue or isolated cells from inner and outer zones, with and without IL-1. Overall, results from both models showed significant modulation of inflammation-related pathways with mechanical stimulation. Anti-inflammatory effects of loading were well-conserved between the tissue compression and cell stretch models for inner zone; however, the cell stretch model resulted in a larger number of differentially regulated genes. Our findings on the global transcriptomic profiles of two models of mechanical stimulation lay the groundwork for future mechanistic studies of meniscus mechanotransduction, which may lead to the discovery of novel therapeutic targets for the treatment of meniscus injuries.

Study on physical and dynamic splitting mechanical properties of temperature-water coupled sandstone

Temperature and water are important factors to induce the mechanical properties of rock mass, the deformation and failure of rock under dynamic load such as blasting depends on its tensile strength. In order to study the influence of temperature and water coupling on the mechanical properties of rock dynamic splitting, the basic physical parameters of sandstone specimens were measured at room temperature and after 45 °C water bath treatment, and the dynamic splitting tensile tests at 8 loading rates were carried out using the Hopkinson pressure bar (SHPB) test apparatus. The results show that the mass and volume of sandstone specimen increased slightly after water bath, but the increase of density was small, and the increase of longitudinal wave velocity was obvious. The dynamic tensile strength and radial dynamic strain of the specimen have a quadratic function relationship with the loading rate, and the positive correlation is obvious, the dynamic tensile strength and radial dynamic strain show strong strain rate effect. The dynamic tensile strength of sandstone specimens after water bath is lower than that under natural condition, but the radial dynamic strain of the specimen after water bath is higher than its natural state. The strain rate increases as a power function of the loading rate, the strain rate of the specimen after water bath is higher than that under natural condition. The failure mode of the specimen after water bath satisfies the condition of validity of Brazilian disc.

General Analytical Solutions for Dynamic Load-Carrying Capacity of Brittle Materials Under an Arbitrary Incident Stress Wave

In this study, two general solutions for the dynamic tensile load-carrying capacity of brittle materials subject to an arbitrary incident stress wave in the form of Fourier integrals are derived. In order to verify the general solutions, we reduce them to three particular solutions, respectively, i.e., trapezoidal pulse, quadratic pulse and cubic pulse. It is found that all of them can well capture the experimental trends in the previous studies. In between, the first two particular solutions can exactly accord with the two previous analytical solutions under the same boundary conditions, respectively. Therefore, for arbitrary tensile boundary pulses, the dynamic tensile strength of the brittle materials can be calculated from static parameters and characteristics of external loading. This study improves the credibility of the previous works that working on deriving the dynamic load-carrying capacity through analytical methods, and thus, consolidate their theoretical foundation. Meanwhile, on basis of the general solution, the relation between the dynamic tensile load-carrying capacity and strain rate can be further deduced by combining static parameters, hence, it could be inappropriate to claim the strain rate effect on tensile strength as an intrinsic material property anymore. In addition, we found that the process to obtain an explicit analytical solution becomes increasingly difficult with the increased complexity of waveform for an incident pulse, or even no explicit solution can be obtained.

Influence of free water on dynamic tensile behavior of ultra-high toughness cementitious composites

The influence of free water on the dynamic tensile behavior of UHTCC was studied using the dynamic Brazilian test. The result showed that the moisture content of the saturated UHTCC reached up to 17%–18% due to their porous properties, which have an influence on their strain rate, splitting tensile strength and dynamic increase factor (DIF). Under the same impact pressure, the dynamic tensile strain rate of saturated UHTCC decreased by 25%–41% compared with that of dry ones. The softening effect of water on the quasi-static and dynamic tensile strength of UHTCC was observed in the study, and the softening coefficients of UHTCC were influenced by the strain rate. The immersion of free water led to the improved strain rate sensitivity of UHTCC, however, the increase in DIF after water infiltration is less significant in the UHTCC than in the steel fiber reinforced concrete and normal concrete under the similar strain rate. The mechanism underlying such phenomenon was discussed.

Strain Field Evolution Characteristics of Free Surface during Crater Blasting in Sandstone under High Stress

Considering the problems related to hard rock blasting under high in-situ stresses at large depths, we conducted crater blasting tests on sandstone specimens under three static load conditions to investigate the strain field evolution of rock blasting under high stress. The digital image correlation (DIC) technique was used to monitor the evolution of the strain field on the free surface. Thus, the influence of the static stress on the blasting strain field was analyzed, and the formation mechanism of cracks on the free surface was elucidated. The results indicate that a circular tensile strain zone was formed without static loading. The direction of the maximum principal strain was perpendicular to the radius, which lead to the random emergence of multiple radial tensile cracks. Under a uniaxial static loading, an elliptical tensile strain zone was formed. The direction of the maximum principal strain was perpendicular to the static loading direction. This facilitated the initiation and propagation of tensile cracks preferentially in the direction parallel to the static loading. Under an equal biaxial static loading, the initial compressive strain in the specimen reduced the increment rate of the blasting strain, and restrained the formation of surface cracks. Besides, a determination method for dynamic tensile fracture strain of rock was proposed.

Study on the dynamic characteristics of rock surrounding a wellbore in energy storage areas during deep geothermal energy mining.

Based on the engineering background in which the rock surrounding a wellbore is affected by a thermal shock, impact disturbances from drilling vibration, cyclic heat extraction and high temperature during hydrothermal geothermal energy mining, the environmental conditions in the shaft wall rock are simulated by means of high temperature, cooling, immersing granite in water with different curing temperatures and applying impact loads. Additionally, an experimental study on the mechanical characteristics of circular granite specimens under radial impact loads and in the heat treatment and water curing conditions is carried out. The results show that the inner diameters of the rings, heating temperatures, curing water temperatures and cycle heating times are less affected than other parameters by the impact load-strain curves of circular granite, which can generally be divided into three sections, i.e., the initial straight stage, nonlinear ascent yield stage and post-peak nonlinear decline stage. The factors in the test weaken the capacity of the circular granite to resist the impact, but the sizes of the inner diameters of the rings play a leading role. Dynamic tensile strain is generated in the inner wall along the impact direction during the impact, while compressive strain is produced on the inner wall in the vertical impact loading direction. By analysing the crack propagation and final failure mode of circular granite, it is found that dynamic tensile failures are generated, crack initiation starts from the inner wall along the impact loading direction, and the outer circle in the vertical direction lags behind. The crack starts early and develops quickly on one side of the transmission bar. Finally, the failure criterion is established on the basis of some assumptions and circular-granite deformation failure characteristics, and the parameters, measured by the Brazilian disk test, are reasonably verified via substitution into the failure criterion equation.

Impact of high UV fluences on the mechanical and sensing properties of polymer optical fibers for high strain measurements.

PMMA-based fibers are widely studied for strain measurements and show repeatable results for Fiber Bragg Gratings (FBGs) inscribed using 325 nm laser and 248 nm laser. However, there is no available material mechanical behavior characterization of the UV source impact on the fiber properties. In this manuscript, fibers are irradiated with high fluence of 325 nm and 248 nm lasers and the fibers properties are investigated using dynamic mechanical analysis and tensile strain for potential use of these fibers past the yield point. It is demonstrated that the UV sources shifted the ultimate tensile strength and changed the strain hardening behavior. Tensile strain measurements show excellent repeatability for gratings inscribed with these two sources with similar sensitivity of 1.305 nm/mɛ for FBG inscribe with 325 nm laser, and 1.345 nm/mɛ for grating written with 248 nm laser in the range 0 to 1.5 % elongation. Furthermore, tests far beyond the yield point (up to 2.8 % elongation) show that grating inscribed with lower UV wavelength exhibit hysteresis. Finally, we demonstrate that 248 nm laser fluence shall be chosen carefully whereas even high 325 nm laser fluence do not critically impact the sensor properties.

Dynamic splitting tensile properties of concrete and cement mortar

AbstractTo investigate the dynamic tensile behaviours of concrete and cement mortar, a 50‐mm split Hopkinson pressure bar was applied on Brazilian disc specimens for dynamic tensile experiments, in which strain rate varied from 10−5 to 20 s−1. The high‐speed camera testing technique was used to capture the dynamic fractured process of the specimens at relative high strain rate. The experimental results revealed that the dynamic tensile strength of concrete specimens has a stronger strain rate effect than that of cement mortar specimens. Then three typical failure patterns of the specimens were confirmed in dynamic experiments. In addition, one‐parameter semi‐empirical relation between dynamic tensile strength and strain rate was established. Finally, the limitation of dynamic splitting experiments on Brazilian disc specimens was discussed in detail at high strain rate, in which the crack initiates from the contact point between the incident bar and specimens rather than the centre of the specimens.

Crack propagation and dynamic properties of coal under SHPB impact loading: Experimental investigation and numerical simulation

To investigate the crack propagation and dynamic mechanical properties of coal under high strain rate loading, 24 sets of Brazilian disk (BD) coal specimens with vertical and horizontal beddings were made, and tests were conducted by a split Hopkinson pressure bar (SHPB) system. Under different impact velocities, a high-frame and high-resolution camera was employed to capture the fracture process, and two high-dynamic strain gauges were used to record the stress pulse signals simultaneously. Using one-dimensional stress wave theory, the dynamic mechanical properties of coal with different bedding directions under different impact velocities were analyzed and discussed. Experimental results indicate that bedding directions not only have a major influence on dynamic mechanical properties such as dynamic tensile strength, strain rate and strain energy but also have a great influence on the crack propagation path. Then, based on the image processing technique and fractal method, cracks conforming to the fractal have been proven, and the results further illustrate that the fractal dimension of cracks on the coal surface increased in the fracture process under SHPB loading. Finally, a numerical model based on bond-based Peridynamic theory was proposed to simulate crack propagation and dynamic mechanical properties of coal under the SHPB test, and the displacement-strain-stress fields were also calculated, which further reveal the fracture mechanism and dynamic behavior of coal under different impact loading conditions.

Regulation of the autophagy-marker Sequestosome1 in periodontal cells and tissues by biomechanical loading.

Orthodontic treatment is based on the principle of force application to teeth and subsequently to the surrounding tissues and periodontal cells. Sequestosome1 (SQSTM1) is awell-known marker for autophagy, which is an important cellular mechanism of adaptation to stress. The aim of this study was to analyze whether biomechanical loading conditions regulate SQSTM1 in periodontal cells and tissues, thereby providing further information on the role of autophagy in orthodontic tooth movement. Periodontal ligament (PDL) fibroblasts were exposed to cyclic tensile strain of low magnitude (3%, CTSL), and the regulation of autophagy-associated targets was determined with an array-based approach. SQSTM1 was selected for further biomechanical loading experiments with dynamic and static tensile strain and assessed via real-time polymerase chain reaction (RT-PCR) and immunoblotting. Signaling pathways involved in SQSTM1 activation were analyzed by using specific inhibitors, including an autophagy inhibitor. Finally, SQSTM1expression was analyzed in gingival biopsies and histological sections of rats in presence and absence of orthodontic forces. Multiple autophagy-associated targets were regulated by CTSL in PDL fibroblasts. All biomechanical loading conditions tested increased the SQSTM1expression significantly. Stimulatory effects of CTSL on SQSTM1expression were diminished by inhibition of the c‑Jun N‑terminal kinase (JNK) pathway and of autophagy. Increased SQSTM1levels after CTSL were confirmed by immunoblotting. Orthodontic force application also led to significantly elevated SQTSM1levels in the gingiva and PDL of treated animals as compared to control. Our invitro and invivo findings provide evidence of a role of SQSTM1 and thereby autophagy in orthodontic tooth movement.

Modeling hyperviscoelastic behavior of elastomeric materials (HDPE/POE blend) at different dynamic biaxial and uniaxial tensile strain rates by a new dynamic tensile-loading mechanism

This article presents a new model developed to investigate hyperviscoelastic behavior of elastomeric materials/polyolefin elastomers (HDPE/POE blend) under dynamic biaxial and uniaxial tensile loading. Various strain energy functions (SEF) have been used in this model, and their capability to predict hyperelastic behavior of the aforementioned materials was validated by experimental data. In the experimental part, a new dynamic tensile-loading mechanism was designed and developed to be mounted on a drop-weight impact-testing machine. As a novelty, this mechanism has the ability to perform either uniaxial or biaxial dynamic tensile tests for any type of material, especially for investigating the hyperviscoelastic behavior of materials like elastomers at various strain rates. In addition, a new hyperviscoelastic model has been developed for elastomeric material, which can predict the behavior of the material well at different strain rates. By increasing the strain rate in the dynamic biaxial and uniaxial loading, Pucci–Saccomandi and Yeoh SEF predicted the dynamic behavior of material well due to its lower root mean square error. In fact, in this case, these functions are more capable than Mooney–Rivlin, Neo-Hookean, and polynomial SEF in predicting the effect of the strain rates. In addition, the results show that Yeoh SEF performs much better than the other SEFs in predicting the material behavior in cases of dynamic biaxial and uniaxial tensile strain. The results also indicated that the newly designed mechanism was capable of performing dynamic tensile loading and extracting its accurate results and could reduce the cost of testing compared to other methods.

Patient‐Specific Hemodynamic Analysis of Coronary Arteries

In cases of severe cardiac stenosis, the selection of treatment options including angioplasty, stent insertion, and bypass surgery are based on cardiac diagnosis provided by electrocardiograms, stress tests, and angiograms. Although these diagnostic tools are all vital, it is still difficult to determine the true extent to which normal blood flow has been compromised. To date, a clear guideline for aggressive intervention does not exist, as stenosis characteristics can vary greatly between patients. Plaque composition, compressibility, and shape are all factors that can modify a patient's risk of incurring a life‐threatening cardiac event in the near future. Our work aims to establish a streamlined computational model that can provide accurate estimation of dynamic shear stress and tensile strain on a plaque based on a patient's specific geometry. Together with flow information provided by 4D cardiac MRI, information from the computational model will allow a cardiologist to make better informed decisions regarding therapeutic options for patient cardiac health.The goal of this undergraduate research project was to determine the most effective method for 3D reconstruction and segmentation of the heart and coronary arteries from patient‐specific CTA (computed tomography angiography) data. The resulting 3D geometry will be imported into COMSOL, a computational fluid dynamics software, for hemodynamics and stress‐strain analysis.Patients' CTA data was provided by the Cardiac Imaging Department of the St. Francis Hospital (with IRB approval). A set of 2097 images were imported into a 3D reconstruction software, 3D Slicer (http://www.slicer.org), and visualized in sagittal, axial, and coronal views. By scanning through images in each plane, major components of the heart (i.e., atria, ventricles, aorta, coronary arteries) were identified manually. 3D reconstruction and segmentation were accomplished using a seeding procedure in which each part of the heart was carefully selected and identified as an individual component. 3D Slicer then generated a 3D‐reconstructed geometry of the heart from seeds. Proper seeding allowed different components of the heart to be visualized individually in the 3D viewer, enabling isolation of the coronary arteries from the whole heart model.Preliminary results showed a 3D model of the whole heart from CTA data with the left main coronary isolated. Manual segmentation was found to be challenging because coronary artery branches are embedded within the cardiac muscle. It was demonstrated to be efficient to refine seeds for coronary artery identification and segmentation by carefully examining the 3D model and performing several iterations of correction. The coronary artery geometry generated in 3D Slicer is then processed by a Vascular Modeling Tool Kit (VMTK, an open source software) to generate the proper geometries (in .stl format) needed for COMSOL, for hemodynamics modeling and analysis.As methods for reconstruction and segmentation are further refined, computational modeling will be used as a high throughput tool to generate useful information on stress/strain conditions within the coronary arteries, moving toward our goal of streamlined personalized cardiac treatment.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Microstructure and Strain Rate-Dependent Tensile Deformation Behavior of Fiber Laser-Welded Butt Joints of Dual-Phase Steels

The microstructure and tensile deformation behavior of the fiber laser-welded similar and dissimilar dual-phase (DP) steel joints over a wide range of strain rates from 10−3 to 103 s−1 were investigated for the further applications on the lightweight design of vehicles. The high strain rate dynamic tensile deformation process and full-field strain distribution of the base metals and welded joints were examined using the digital image correlation method and high-speed photography. The strain rate effects on the stress–strain responses, tensile properties, deformation, and fracture behavior of the investigated materials were analyzed. The yield stress (YS) and ultimate tensile strength (UTS) of the dissimilar DP780/DP980 welded joints were lying in-between those of the DP780 and DP980 base metals, and all materials exhibited positive strain rate dependence on the YS and UTS. Owing to the microstructure heterogeneity, the welded joints showed relatively lower ductility in terms of total elongation (TE) than those of the corresponding base metals. The strain localization started before the maximum load was reached, and the strain localization occurred earlier during the whole deformation process with increasing strain rate. As for the dissimilar welded joint, the strain localization tended to occur in the vicinity of the lowest hardness value across the welded joint, which was in the subcritical HAZ at the DP780 side. As the strain rate increased, the typical ductile failure characteristic of the investigated materials did not change.

Dynamic response of a Q&P steel to high-strain-rate tension

The experimental study on the volume fraction of retained austenite for QP980CR steel under high-strain-rate tension is briefly described. An interrupted tensile split Hopkinson bar (TSHB) is developed to control the elongation of specimens. The QP980CR steel samples recovered from the interrupted TSHB tests are investigated using synchrotron X-ray diffraction (XRD) to analyze the effects of strain and strain rate on the martensitic transformation of retained austenite. A constitutive model of QP980CR steel coupling with the transformation-induced plasticity (TRIP) effect is presented based on Delannay's mean-field modeling. The stress–strain curves of quasi-static and dynamic tensile tests for QP980CR steel are compared with the results predicted by the presented constitutive model. The diffuse necking of QP980CR steel sheet specimens in TSHB tests is analyzed using Batra and Wei's instability criterion and the presented constitutive model. The effects of strain rate and temperature on the dynamic tensile fracture strain of QP980CR steel are also given.

Cardiomyogenesis of periodontal ligament-derived stem cells by dynamic tensile strain.

Cellular therapies for the treatment of myocardial infarction have proven to be an invaluable tool in recent years and provide encouraging evidence for the possibility to restore normal heart function. However, questions still remain as to the optimal cell source, pre-conditioning methods and delivery techniques for such an application. This study explores the use of a population of stem cells arising from the neural crest and isolated from adult human periodontal ligament along with short-term mechanical strain as an inducer of cardiomyogenesis and possibly pre-conditioning stimulus for cellular cardiomyoplasty. Cells were subjected to a short-term dynamic mechanical tension in our custom-built bioreactor and analyzed for cardiomyogenic commitment. Mechanical strain elicited a cardiomyogenic response from the cells following just 2h of stimulation. Mechanical strain activated and translocated cardiac-specific transcription factors GATA4, MEF2C and Nkx2.5, and induced expression of the sarcomeric actin and cardiac troponin T proteins. Mechanical strain induced production of significantly higher levels of nitric oxide when compared to static controls. Elimination of elevated ROS levels by free radical scavengers completely abolished the cardiomyogenic response of the cells. MicroRNA profile changes in stretched cells were detected for 39 miRNAs with 16 of the differentially expressed miRNAs related to heart development. The use of stem cells in combination with mechanical strain prior to their delivery in vivo may pose a valuable alternative for the treatment of myocardial infarction and merits further exploration for its capacity to augment the already observed beneficial effects of cellular therapies.

(Invited) Strain Sensing Inverter and Photovoltaic Circuits Based on Novel Heptazole Organic Thin Film

Following solid pentacene films and other p-type small molecules, in the present work, we show a new small molecule, 8,16-dihydrobenzo[a]benzo[6,7]indolo[2,3-h]carbazole (heptazole; C26H16N2) which has almost the same HOMO level as that of pentacene but with a higher HOMO-LUMO gap of ~2.95 eV, so as to be photostable under visible light except deep blue-to-violet range. The field-effect mobility of our new OTFT turns out to be ~0.21 cm2/V s which is lower than that of the pentacene OTFT on the same dielectric layer, however our new OTFT on flexible substrate is found to work as a strain sensor because organic heptazole layer changes its electric resistance under tensile strain but such change appears elastically recoverable by removing the strain. We here display an inverter which is composed of two OTFTs but with 90 drgree different channel orientations each other: one would work as a strain sensor while the other works as a load under static and dynamic tensile bending strain conditions. Moreover, we also found that our heptzole organic film has very small exciton binding (~40 meV) properties under deep blue photons (wave length~410 nm). Taking advantages of such small exciton binding energy, we developed a Schottky diode circuit which can dynamically measure the photovoltaic effects without any assistacnce of electric power. Based on above-mentioned benefits of our heptazole layer in TFT and Schottky diode, we demonstrate in the meeting the dynamic strain sensing of the organic inverter on flexble substrate, and dynamic photovoltaic switching of the Schottky diode circuits as briefly shown below. Figure 1

Barrier property and mechanical flexibility of stress controlled organosilicon/silicon oxide coatings on plastic substrates

In this study, we demonstrated the effect of the organosilicon layer in the pairs of the organosilicon/silicon oxide (SiOx) multi-layered structure on the barrier property to water vapor permeation and on the mechanical flexibility under tensile strain. The residual internal stress in the structure was controlled by introducing the organosilicon layer, thereby enhancing the structural barrier property. The experimental results showed that the thickness of the organosilicon layer required in each paired structure to minimize the structural stress was closely correlated to the surface and material properties of the underlying layer. Accordingly, the internal stress that existed in the 2- and 3-paired structures, as well as their barrier properties to the water vapor permeation, was optimized further by altering the thickness of the organosilicon layer that was deposited onto the surface of the SiOx film. These pairs of multi-layered structures, in which the compressive stress had been minimized, cracked at a lower bending radius under static tensile strain than the SiOx film with the same thickness deposited directly onto the polyethylene terephthalate (PET) substrate. In addition, the degradation in the water vapor transmission rate (WVTR) of the organosilicon/SiOx multi-layered structure deposited onto the PET substrate was less apparent than that of the PET coated only with a single SiOx film. This was ascribed to the structure having fewer cracks than the single SiOx film after being bent by the same tensile strain. Dynamic tensile strain also was conducted on these multi-layered structures to further confirm the structural reliability.