Tensile Failure Strain Research Articles

Static and Fatigue Tensile Properties of Cross-Ply Carbon-Fiber-Reinforced Epoxy-Matrix-Composite Laminates with Thin Plies

Carbon-fiber-reinforced epoxy-matrix composite (CFRP) laminates with thin plies have strong damage-resistance properties compared with standard prepregs. The static and fatigue tensile fracture behavior of cross-ply CFRP laminates with thin plies should be further studied to establish the applicability of thin-ply prepregs for industrial structures. In this study, the static and fatigue tensile properties of cross-ply, high-strength polyacrylonitrile (PAN)-based carbon-fiber (T800SC)-reinforced epoxy-matrix composites with thin plies were investigated. The fiber orientations of the CFRP specimens were set to cross-ply with [0/90]10S (subscript S means symmetry), [(0)5/(90)5]2S, and [(0)10/(90)10]S. The static and fatigue tensile characteristics of the cross-ply CFRPs with thick plies with [0/90]2S and [(0)2/(90)2]S were also investigated for comparison. Under static loading, the tensile strength and failure strain of the thinnest 90°-ply-CFRP specimens were more than 5% higher than those of the other 90°-ply-thickness specimens. However, the tensile moduli and Poisson’s ratios were comparable between the cross-ply CFRPs with thin and thick plies. Under fatigue loading, the fatigue responses of the thinnest 90°-ply-CFRP specimens were 3% higher than those of the other 90°-ply-thickness specimens during lower-fatigue-cycle testing (<105 cycles). However, during higher-fatigue-cycle testing (>105 cycles), the fatigue responses decreased, with a decrease in the 90°-ply thickness, and the fatigue characteristics of the thinnest 90°-ply-CFRP specimen were 7% lower than those of the other cross-ply thin- and thick-ply-CFRP specimens.

Molecular Dynamics Study on Mechanical Properties of CO2–N2 Heteroclathrate Hydrates

One of the key issues in the exploitation of natural gas hydrates is the geo-mechanical stability of hydrate-bearing sediments. Herein, based on classical molecular dynamics simulations, we have investigated the mechanical stability of CO2–N2 heteroclathrate hydrates (CNHHs) under uniaxial loading. The results show that the ratio of CO2 to N2 in the large and small water cages has a crucial effect on the mechanical properties and fracture behaviors of CNHHs. In most cases, CNHHs show brittle fracture behavior, and their ultimate tensile strength, failure strain, and Young’s modulus decrease significantly with the increase of CO2 ratio in small cages. However, when the small cages are all occupied by CO2, CNHHs display ductile fracture behavior. In particular, the CNHHs with a CO2 fraction of 0.75 have their hydrated cages broken by amorphization with increasing strain. The effect of CO2 molecules occupying the different types of water cages on fracture behavior has been discussed in detail. The results indicate that the occupancy of small cages by CO2 plays a decisive role in the fracture position. In the case of the nearest-neighbor large cages, the fracture positions are consistent with the positions of CO2 molecules with a high probability. The lattice distortion caused by the occupancy of the water cage by CO2 is the key factor affecting fracture behavior. These results should be helpful in understanding the deformation and fracture mechanisms of heteroclathrate hydrates as well as in assessing the impact of CH4–CO2/N2 replacement and CO2 sequestration on the geological stability of gas hydrate reservoirs.

Effects of single-phase and co-deposited interphases on mechanical properties of T700TM-C/SiC minicomposites: experiment and theory prediction

ABSTRACT Experimental and theory investigations on the effects of single-phase (PyC) and co-deposited (PyC+SiC) interphases on the mechanical properties of T700TM-C/SiC minicomposites were conducted. Monotonic tensile tests and fiber’s push-in tests were conducted to obtain the minicomposite’s macro tensile mechanical properties and micro interface properties. The tensile strength was analyzed via a two-parameter Weibull distribution. The failure mechanism was obtained by fiber’s push-in tests and characterized by fracture morphology, and a damage-based micromechanical constitutive model was adopted to predict the tensile stress-strain response and interface debonding ratio (η) of C/SiC minicomposites with different interphases. For C/SiC, the experimental tensile curves were linearly till final tensile fracture with the lowest tensile strength and failure strain, due to the low interface shear strength (i.e., τ iss = 50.8 ± 15.3 MPa). For C/(PyC)300 nm/SiC, the minicomposite with the moderate ISS (i.e., τ iss = 62.2 ± 5.9 MPa) possessed the highest tensile strength and failure strain with the highest interface debonding ratio (i.e., η max = 0.95). For C/(PyC+SiC)/SiC, the tensile strength and strain were both lower than those of C/(PyC)/SiC due to the lower η.

Overcoming strength–ductility trade-off of nanocrystalline metals by engineering grain boundary, texture, and gradient microstructure

The strength–ductility trade-off has been a long-standing dilemma for polycrystalline metals. Though many strategies such as introduction of gradient and twinned microstructure have been proposed to overcome the strength–ductility trade-off of nanocrystalline (NC) metals, a higher strength–ductility synergy is always called for. Here schemes taking advantage of texture engineering with incorporation of grain boundary (GB) strengthening and gradient microstructure design are proposed to achieve a more desirable strength–ductility synergy. Taking into account the size-dependent storage of dislocations in grains, GB sliding, and evolution of the void volume fraction, crystal plasticity finite element simulations incorporating the Gurson-type model are performed to reveal the mechanisms underlying the low ductility and strength–ductility trade-off of NC metals. Low GB strength and nonmonotonic variation of dislocation storage ability with respect to the grain size are revealed as the dominant factors responsible for the low ductility and the strength–ductility trade-off in NC metals. The speculation that there exists a most brittle grain size for NC metals is confirmed. It is also found that the ductility of NC metals is governed by the GB damage and the ability of intragranular dislocation storage at high GB strength. Moreover, it is shown that the failure tensile strain for cube-textured NC copper at a certain grain size could be more than twice the failure tensile strain for untextured one at high GB strength.

Optimization Design of Asphalt Mixture Composite Reinforced with Calcium Sulfate Anhydrous Whisker and Polyester Fiber Based on Response Surface Methodology.

In order to improve the properties of calcium sulfate anhydrous whisker (ACSW) and polyester fiber composite reinforced asphalt mixture (ACPRA) to meet the service requirements of pavement materials in low-temperature environments, the central composite circumscribed design (CCC), a kind of response surface methodology, was chosen to optimize the design parameters. Three independence variables, asphalt aggregate ratio, ACSW content, and polyester fiber content were adopted to evaluate the design parameters. Four responsive variables, air voids, Marshall stability, splitting tensile strength, and failure tensile strain, were chosen to study the volumetric and mechanical characteristics, and the low-temperature behavior of ACPRA by the Marshall test and indirect tensile test at -10 °C. The results showed that, taking low-temperature behavior optimization as the objective, the CCC method was practicable to optimize design of ACPRA, and the optimization design parameters were asphalt aggregate ratio of 4.0%, ACSW content of 10.8%, and polyester fiber content of 0.4%. Furthermore, the impact of three independence variables interactions on four response variables was also discussed, and it was identified that the interaction between asphalt aggregate ratio and ACSW content, and between asphalt aggregate ratio and polyester fiber content, has greater bearing on the splitting tensile strength and failure tensile strain of APCRA. Meanwhile, ACSW and polyester fiber enhancing the low-temperature behavior of APCRA was primarily connected with their contents.

Molecular insights into the temperature and pressure dependence of mechanical behavior and dynamics of Na-montmorillonite clay.

Sodium montmorillonite (Na-MMT) clay mineral is a common type of swelling clay that has potential applications for nuclear waste storage at high temperatures and pressures. However, there is a limited understanding of the mechanical properties, local molecular stiffness, and dynamic heterogeneity of this material at elevated temperatures and pressures. To address this, we employ all-atomistic (AA) molecular dynamics (MD) simulation to investigate the tensile behavior of Na-MMT clay over a wide temperature range (500 K to 1700 K) and pressures (200 atm to 100 000 atm). The results show that increasing the temperature significantly reduces the tensile modulus, strength, and failure strain, while pressure has a minor effect compared to temperature, as seen in the normalized pressure-temperature plot. Mean-square displacement (MSD) analysis reveals increased molecular stiffness with increasing pressure and decreasing temperature, indicating suppressed atomic mobility. Our simulations indicate temperature-dependent dynamical heterogeneity in the Na-MMT model, supported by experimental studies and quantified local molecular stiffness distribution. These findings enhance our understanding of the tensile response and dynamical heterogeneity of Na-MMT clay under extreme conditions, aiding the development of clay minerals for engineering applications such as nuclear waste storage and shale gas extraction.

Characterization of graphene reinforced 3C-SiC composite as a metal-free friction material using molecular dynamics simulation

In this work, the tribological, mechanical and thermal properties of graphene (Gr)-based 3C-SiC nanocomposite as a metal-free friction material were first studied by using molecular dynamics (MD) simulations. In tribological properties, the frictional force, normal force, effective coefficient of friction and wear rate were investigated. The effects of scratching depth, temperature, scratching velocity and the number of Gr layers in the composite to the friction process were considered. Young’s modulus, ultimate tensile stress (UTS) and failure strain in the mechanical properties, and thermal conductivity in the thermal property were also included to understand the tribological performances of the composite. The interfacial interaction energy was evaluated to characterize the effect of interface on material properties. The validations were performed on some representative results. In the simulation results with the selected configurations which are listed in the subsequent content, the nanocomposite showed the lowest wear rate with an appreciable coefficient of friction at the scratching depth of 10 Å. 10 m/s was the optimal scratching speed to maintain the best wear performance. A temperature of 300 K yielded the highest coefficient of friction and the lowest wear rate. The model with three Gr layers showed a relatively high coefficient of friction and a relatively low wear rate. The model with five Gr layers stacked in 3C-SiC exhibited the best mechanical performance. The nanowire model with two Gr layers showed a higher thermal conductivity. The research findings will provide guidance in design and manufacturing of Gr/3C-SiC friction materials. The study will also help understand the effect of Gr as a potential reinforcement for metal-free friction materials.

Structural analysis of experimentally fabricated glass fiber reinforced (GFRP) composites

Engineering materials play major role in the production system with wide applications since ancient periods till today. Engineering materials like metals, non-metals, ceramics, plastics and composites are selected based on their properties suitable in the field of applications. GFRP are compared to the fiber glass material, GFRP wide real time applications as in case of research laboratories,MRI units, manufacturing critical impact parts, home build equipments like interior works, high fatigue purposes and high compressive structural equipment designs. Composite materials have wide range of structural applications in engineering fields also. In this work, glass fiber reinforced composite material (GFRP) with different layers of laminates is prepared as per the required dimensions and experiments are conducted for structural analysis of GFRP composite material. The present research work the Mechanical structural analysis conducted. The experimental results also reveal that plays a significant role in the enhancement of mechanical properties such as tensile strength, failure strain, and hardness. Again the experimental properties obtained for GFRP material from statistical tests are compared with its theoretical properties. Also the properties of GFRP are compared with the other composite materials to have real time applications of fiber glass material. The experimental results indicated an outstanding improvement in the tensile, impact, and flexural properties of hybrid composite materials. The results showed Young’s modulus of 25.42 GPa, and maximum bending deflection attained at yield stress of 133 MPa with ultimate tensile stress of 533 MPa.

Structural and biomechanical characterizations of acellular porcine mitral valve scaffolds: anterior leaflets, posterior leaflets, and chordae tendineae.

Mitral valve (MV) tissue engineering is still in its early stage, and one major challenge in MV tissue engineering is to identify appropriate scaffold materials. With the potential of acellular MV scaffolds being demonstrated recently, it is important to have a full understanding of the biomechanics of the native MV components and their acellular scaffolds. In this study, we have successfully characterized the structural and mechanical properties of porcine MV components, including anterior leaflet (AL), posterior leaflet (PL), strut chordae, and basal chordae, before and after decellularization. Quantitative DNA assay showed more than 90% reduction in DNA content, and Griffonia simplicifolia (GS) lectin immunohistochemistry confirmed the complete lack of porcine α-Gal antigen in the acellular MV components. In the acellular AL and PL, the atrialis, spongiosa, and fibrosa trilayered structure, along with its ECM constitutes, i.e., collagen fibers, elastin fibers, and portion of GAGs, were preserved. Nevertheless, the ECM of both AL and PL experienced a certain degree of disruption, exhibiting a less dense, porous ECM morphology. The overall anatomical morphology of the strut and basal chordae were also maintained after decellularization, with longitudinal morphology experiencing minimum disruption, but the cross-sectional morphology exhibiting evenly-distributed porous structure. In the acellular AL and PL, the nonlinear anisotropic biaxial mechanical behavior was overall preserved; however, uniaxial tensile tests showed that the removal of cellular content and the disruption of structural ECM did result in small decreases in maximum tensile modulus, tissue extensibility, failure stress, and failure strain for both MV leaflets and chordae.

Preparation and properties of chitin/silk fibroin biocompatible composite fibers

In the present world chitin is used enormously in various fields, such as biopharmaceuticals, medical and clinical bioproducts, food packaging, etc. However, its development has been curbed by the impaired performance and cumbersome dissolution process when chitin materials are dissolved and regenerated by physical or chemical methods. To further obtain the regenerated chitin fiber material with improved performance, silk fibroin was introduced into the chitin matrix material, and chitin/silk fibroin biocompatible composite fibers were obtained by formic acid/calcium chloride/ethanol ternary system and top-down wet spinning technology. The produced composite fibers outperformed previously reported chitin-silk composites in terms of the tensile strength (160 MPa) and failure strain (25%). The fibers also performed good cell compatibility and strong cellular affinity for non-toxicity. The cell viabilities of the fibers were about 20% greater than those of silk fiber after three days of co-culture with NIH-3T3. Furthermore, no hemolysis occurs in the presence of chitin/silk fibers, demonstrating their superior hemocompatibility. The fibers had a hemolysis index as low as 1%, which is far lower than the acceptable level of 5%. The material offers prospective opportunities for biomaterial applications in anticoagulation, absorbable surgical sutures, etc.

The influence of microstructure on the tensile properties of a creped tissue paper: Modeling and experiments

Low density tissue papers are soft fiber networks with a folded internal microstructure—deliberately imparted during a widely used manufacturing process, called dry creping. The folded crepe structure enhances a tissue paper’s specific volume, stretchability, and softness. The influence of the micron-scale crepe structure on nonlinear tensile response is studied using experiments and a discrete elasto-plastic model (DEM). First, ‘Crepe Index (CI)’ is defined to quantify the crepe structure. An optical method to obtain high resolution edge images is developed to measure the CI. The relationship between the CI and tensile failure strain and initial elastic stiffness is assessed: the failure strain is observed to be proportional to CI, while the dependence of initial stiffness on CI is unclear–presumably due to the damage induced through the de-densification of fiber layers during the manufacturing. The effect of CI on initial stiffness and failure strain is assessed using DEM by idealizing the creped paper as a segmented triangular wave—each segment governed by a bilinear elastoplastic constitutive law and a strength-based failure criterion. The model reveals that the initial stiffness of a creped sheet depends not only on the CI but also on sheet-thickness to crepe-wavelength ratio, and the stiffness of the uncreped sheet. The failure strain is found to be stretching dominated at low CI, and bending dominated at higher CI. Qualitative agreement is found between the DEM and experiments. The significance of both the material and the geometric non-linearity on the macroscale tensile response of a creped tissue paper emerges from this study.

Tensile mechanical properties of vitrified porcine menisci are superior to frozen and similar to fresh porcine menisci

Vitrification inhibits crystallization of ice and may allow the mechanical properties of menisci to be preserved for transplantation without the damaging consequences of ice crystals formed during freezing. The primary objective of this study was to investigate the differences between fresh, frozen, and vitrified porcine lateral menisci examining tensile mechanical properties along the circumferential-peripheral, circumferential-central, longitudinal, and radial orientations. The secondary objective was to investigate the variations in the tensile mechanical properties of menisci comparing the circumferential-peripheral orientation to the three other orientations: circumferential-central, longitudinal, and radial. Quasi-static tensile testing was conducted to quantify the tensile mechanical properties of fresh, frozen and vitrified menisci. Ultimate tensile strength of frozen menisci were significantly decreased compared with fresh and vitrified menisci along three orientations: circumferential-peripheral, longitudinal, and radial. Along the circumferential-central orientation, tensile modulus of frozen menisci was significantly decreased compared with fresh menisci. The mechanical properties of vitrified menisci were comparable to fresh menisci along all four orientations. For all menisci (fresh, frozen and vitrified), ultimate tensile strength and failure strain along the circumferential-peripheral orientation were significantly increased compared with the three other orientations. Freezing was detrimental to the mechanical properties of menisci but vitrification likely avoided the negative effects of freezing thereby preserving mechanical properties that were comparable to fresh menisci. The findings of this study revealed that vitrification was superior to freezing for preserving mechanical properties of meniscal tissue; hence, vitrification is likely to be a competitive alternative to freezing for meniscal transplantation in the future.

Tensile behavior of the titanium-steel explosive welded interface under quasi-static and high-strain rate loading

Explosive welding is well known for its capability to join a wide variety of both similar and dissimilar metals. The strengths of the welded composite plates are largely influenced by the bonding strengths of the welding interfaces, which generally exhibit a periodic wavy shape. The measurement of the tensile properties of the bonding interface is challenging due to the difficulties in preparing conventional direct tensile specimens arising from the millimeter-sized thickness of the flyer plate. In this paper, a novel small-sized (15 mm × 14 mm × 8 mm) double-T-shaped specimen was designed to study the tensile properties and failure mechanisms of the titanium/steel bonding interface, in which a clamping apparatus was used to apply compressional load on the specimen to generate tensile stress. The quasi-static (∼0.001/s) tension was conducted using the Instron MTS and the high strain rate (2000–5000/s) tension was performed using the split Hopkinson pressure Bar apparatus. Further, the microstructure of interfacial zone was characterized by optical microscopy, scanning electron microscopy and energy dispersive spectrometer. The experimental results indicated that the interface strength increased with increasing strain rate, showing an obvious positive strain rate effect. The fluctuation in tensile strengths and failure strain of the titanium/steel bonding interface were due to the presence of non-uniform defects, (e g. cavities, cracks and brittle intermetallic etc.) formed on the bonding interface. Those defects as discontinuities and stress concentration points would result in degraded mechanical properties. The fracture morphology mainly reveals brittle fracture under quasi-static, while ductile fracture existed in some zone at high strain rate. Failure mainly occurred in the bonding interface near the steel side from the interface, which showed microcracks, cleavage plane, tearing ridges, dimples, fragmentation of brittle intermetallic compounds. Meanwhile, the double-T-shaped specimen has proven to be effective to measure the tensile mechanical properties of the interface of materials with small thickness.

Predicting uniaxial tensile strength of expansive soil with ensemble learning methods

Tensile stress is a major parameter controlling the desiccation cracking, which may incur the tensile failure of expansive soil slopes. In this study, a series of experiments was performed and a dataset of 125 records was initially recorded with 6 features viz., dry density (DD), water content (W), matric suction (MS), unconfined compressive strength (UCS), failure compressive strain (FCS) and the failure tensile strain (FTS) and 1 label, uniaxial tensile strength (UTS). Three classical ML methods and three ensemble methods viz., random forests, extreme gradient boosting, and the stacked generalization, were utilized to capture the relationships between the label and the features. The experimental results show that the tensile strength of the expansive soils is subject to the coupling effects of the UCS, the W and the FTS. And their relative importance to the uniaxial tensile strength can be discerned by the top performing models as UCS (40.18%) > W (36.46%) > FTS (23.36%). The stacked generalization can effectively integrate the merits of the other 5 ML methods, and, hence, provides the most accurate prediction of UTS for the given dataset.

Tensile failure strain and microstructure of unidirectional carbon fibre non-crimp fabric composites

UD non-crimp fabric (NCF) carbon/epoxy composites were tested in longitudinal tension to assess the influence of the stitching on the tensile failure strain of the carbon fibre layers. The composites made with the stitched layers had the same tensile failure strain as the reference non-stitched layer composite. A composite where the stitching yarns has been removed appears to have a lower failure strain though. Computed tomography images revealed that the regions adjacent to the stitch showed the highest fibre volume fraction. The stitched layers clearly showed a higher fibre misalignment than the non-stitched layers. The fibre misalignment was very low in the layers in which the stitches were removed. The observations suggest that the fibre distortions due to stitching do not reduce the failure strain; the distortions caused by removing the stitches are detrimental and reduce the failure strain.

Probing the stochastic fracture behavior of twisted bilayer graphene: Efficient ANN based molecular dynamics simulations for complete probabilistic characterization

The present article outlines a probabilistic investigation of the uniaxial tensile behaviour of twisted bilayer graphene (tBLG) structures. In this regard, the twist angle (θ) and temperature (T) are considered as the control parameters and the ultimate tensile strength (UTS) and failure strain of the tBLG structures are considered as the responses. It is observed that with the increase in twist angle (θ) of tBLG; the fracture responses exhibit a declining trend deterministically. The tBLG twisted with the magic angle (θ = 1.08o) results in around 7% decrease in UTS and nearly 24% decrease in failure strain, when compared with normal BLG (θ = 0̊). The Monte Carlo simulation (MCS) based random sampling is performed for the considered control parameters, wherein θ is varied from 0o to 30o, and temperature is varied from 100 K to 900 K. Within such bounds of the input parameters, the training (64 samples) and validation (8 samples) sample spaces are constructed. In the next step, molecular dynamics (MD) simulation of uniaxial tensile deformation of the modelled tBLG structures is carried out for each instance of the sample space. The dataset is subsequently used to form and validate the artificial neural network (ANN). The computationally efficient machine learning (ML) model is further utilized to perform the detailed investigation of fracture behaviour of the tBLG structures in the probabilistic framework. Such analysis captures all the possible instances of variation in the input parameters and leads to deep insights in the material behaviour, which would have otherwise remained unnoticed due to the prohibitive nature of conducting a large number of MD simulations. The novelty of the present study lies in the probabilistic interpretation of the tensile behaviour of tBLG structures subjected to variation in twist angle (θ) and temperature (T). The preparation of nano-scale samples with the exact design specifications such as twist angle is often extremely difficult, which leads to inevitable stochastic system disorders. The current article essentially proposes a probabilistic avenue of quantifying the effect of such disorders on the failure properties of tBLG.

Vakum Destekli Reçine İnfüzyon Kalıplama ile Üretilmiş Twaron®/Epoksi Lamine Kompozit Plakaların 9 mm Mermi Tehdidine Karşı Balistik Performansı Üzerine Sayısal Çalışma

This article presents the experiments on the ballistic effect of plates formed by stacked Twaron® fabrics between 10 and 16 layer numbers impregnated with epoxy resin by vacuum infusion method and the results of Autodyn-2D® simulations using an axisymmetric model. The ballistic impact resistance of the panels produced was determined according to the NIJ-STD-0108.01 standard. All panels were tested against 9 mm FMJ bullets at an average velocity of 390 m/s with the MP5 gun for armour application. The interaction of the plates with the bullet, the post-shot damage photographs, residual velocities of the bullet were compared with Autodyn-2D® simulations. Parametric study was performed in the analysis to determine the optimum bullet velocity, layer thickness and tensile failure strain. It was observed that the data obtained from the simulations were consistent with the experiments.

Static and dynamic tensile behaviors of BFRP bars embedded in seawater sea sand concrete under marine environment

Basalt fiber reinforced polymer (BFRP) bars can be used as an appropriate substitute for steel rebars in marine concrete structures due to their corrosion-free nature and high tensile performance. However, the long-term dynamic properties of BFRP bars in the marine environment are not well known, which is critical for structural safety when subjected to external dynamic loads (e.g., tsunamis and earthquakes). Therefore, this study investigates the static and dynamic tensile behaviors of BFRP bars after exposure to the seawater sea sand concrete (SWSSC) under marine environment. Accelerated corrosion tests were conducted under various exposure periods (60, 90, and 120 days) and temperatures (25, 40, and 55 °C). Both optical stereo microscope (OSM) and scanning electron microscope (SEM) were used to examine the failure patterns of BFRP bars, whereas the degradation mechanisms were investigated by X-ray micro-computed tomography (micro-CT), SEM, and Fourier transform infrared spectroscopy (FTIR). Results show that the tensile properties of BFRP bars are sensitive to strain rate. Both the tensile strength and the elastic modulus of BFRP bars increase with increasing strain rate, but the failure strain drops. The tensile strength and failure strain reduce with increasing exposure temperature and duration, whereas the elastic modulus does not change significantly. Microstructure analysis clearly reveals that failures of BFRP bars occur due to fiber breakage, matrix cracking, and interface debonding. The basalt fibers always exhibit brittle fracture, but the fracture surfaces change from relatively flat to rough when the strain rate increases. Moreover, the deterioration of BFRP bars is caused by resin hydrolysis, fiber-resin interfaces debonding and fiber damage after corrosion. These results can provide some insights to promote the application of BFRP composites in coastal and marine structures.

Synergistic fracture toughness enhancement of epoxy-amine matrices via combination of network topology modification and silica nanoparticle reinforcement

A strategy for enhancing fracture toughness of nanosilica particle (NSP) reinforced high T g epoxy thermosets via topological rearrangement of cross-linked networks is presented. Hybrid systems consisting of NSP with an average particle size of 20 nm and monoamine functionalized partially reacted substructures (mPRS) were prepared using high T g tetraglycidyl ether of diaminodiphenylmethane (TGDDM) and a low T g diglycidyl ether of bisphenol A (DGBEA) epoxies cured with Jeffamine D230. A synergistic effect on fracture toughness improvement was observed for all hybrid systems. For the high T g TGDDM system, the fracture energy of the base epoxy polymer showed a moderate increase from 119 J/m 2 to 203 J/m 2 with the addition of 10 wt% NSP. Modifying the network topology of this system using 15 wt% mPRS tripled the fracture energy to 652 J/m 2 . It was found that the addition of mPRS results in hybrid modified systems capable of exceptional tensile failure strains, thus significant plastic shear deformation is induced near the crack-tip region enhancing NSP debonding and subsequent void growth and energy dissipation . Fracture morphologies of the hybrid systems using scanning electron microscope (SEM) showed increasing number of voids and enhanced void growth with increasing weight ratio of mPRS. Impact tests showed the role of these toughening mechanisms on high strain rate deformation and energy dissipation.

Evaluation on the Performance of Hydraulic Bitumen Binders under High and Low Temperatures for Pumped Storage Power Station Projects.

The high and low-temperature performance of five hydraulic bitumen binders was evaluated using the dynamic shear rheometer (DSR) test, infrared spectrum test and direct tensile (DT) test. These hydraulic bitumen binders were respectively applied for several pumped storage power stations (PSPS) projects that were constructed or under construction. In order to relate the bitumen performance to the mixture performance, the slope flow test, three-point bending test and thermal stress restrained specimen test were carried out on hydraulic asphalt mixtures. The test results indicated the DSR rheological master curves can well distinguish the difference of each bitumen binder as well as the effect of polymer modification. Phase angle master curves, black diagrams and infrared spectra all indicated that several penetration-grade hydraulic bitumen binders were not virgin bitumen binders but were modified with relatively lower SBS polymer content when compared with traditional SBS-modified bitumen. When selecting the commonly used Karamay SG70 hydraulic bitumen as a reference, the normal SBS-modified bitumen was superior to other bitumen in terms of low- and high-temperature performance. Several slightly SBS-modified bitumen binders did not always show consistent results, which indicated that slightly modified bitumen may not really have the desired performance as expected. Therefore, SBS-modified bitumen will be more promising when dealing with extremely low or high temperatures. Bitumen performance was well compared with the mixture performance by using the bitumen creep, relaxation and tensile failure strain corresponding to the asphalt concrete slope flow, the maximum bending strain and the failure temperature, respectively. Compared with the traditional penetration, softening point and ductility test, it indicated that the DSR rheological test, creep test, direct tensile test and stress relaxation test can be used as more powerful tools for the characterization and optimization of hydraulic bitumen binders.