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The metallic bone fracture fixation plates are progressively being replaced by epoxy-reinforced glass fiber laminates (ERGFL) due to a higher strength-to-weight ratio and near neat shape manufacturing. Bone fracture fixation laminates are required to sustain the cyclic load due to the physical movement of the body. Therefore, the characterizations of glass fiber/epoxy laminates with drilled holes are important to study. Despite extensive research on the mechanical characterization of composite laminates, several unique circumstances remain unexplored, such as the characterization of glass fiber/epoxy laminates with drilled holes. The drilling laminates weakened the laminates' mechanical strength and damaged the area around the drilled hole. With Jo drill point designs, the greatest thrust forces (0.56 kN) were observed at 2800 rpm of cutting speed and 0.19 mm/rev of feed rate. Among the various drill points used, the drilled ERGFL laminates with Jo drill had the maximum fatigue life cycle of 87×10³. [ABSTRACT FROM AUTHOR]

The damage mechanism of 2D woven fiberglass panels under random vibration loadings was investigated by means of an experimental analysis and compared with the damage mechanism under constant-amplitude loadings. Based on experimental observations, it was found that the failure mode under vibration loadings was delamination, and predicting the vibration fatigue life using the traditional S – N curve would result in significant errors. Therefore, a prediction method was proposed to accurately estimate the vibration fatigue life of a 2D woven fiberglass panel by modifying the conventional S – N curve. An experimental verification showed that this method has a high level of prediction accuracy. [ABSTRACT FROM AUTHOR]

To investigate the fatigue performance of perforated and bolted pultruded Glass Fiber Reinforced Polymer (GFRP) laminates, a series of tests are conducted including static tensile and cyclic fatigue test, while Digital Image Correlation (DIC) and CT tests were implemented to monitor strains around the perforations and damage developed in the samples subjected to tensile and fatigue tests respectively. The stress concentrations of the cyclic loaded perforated GFRP laminates are discussed based on the experiment results. Due to the stress limitation of single bolted laminates, the diameter to width ratio is suggested to be less than 0.3. The GFRP laminates with double holes have a better fatigue performance than that of single hole, which is called the double-hole effect. This effect is also found in double bolted GFRP laminates. Considering the strength of the laminates between the holes and to unify the requirement, the critical distance to width ratio is suggested to be 1.6 and the diameter to width ratio should be less than 0.3. [ABSTRACT FROM AUTHOR]

A composite material based on a polyester resin and fiberglass reinforcement was fabricated by the contact molding process with a fiber percentage of 40%. This material underwent a cyclic fatigue loading and 3-point bending at slow speed. The experimental results were used to plot the S–N curve based on a linear function, Hwang & Han's relation and Basquin's hypothesis. A probabilistic analysis based on the Weibull distribution with two and three parameters was used in order to adjust and predict the fatigue behavior of the material used in the study. This analysis made it possible to plot the fatigue curve for different levels of reliability (Ps = 99%, Ps = 90%, Ps = 50%, Ps = 36.8% and Ps = 10%), in order to identify first time to failure for material reliability and safety limits. [ABSTRACT FROM AUTHOR]

This work compares the tensile and fatigue behavior of unidirectional glass fiber/epoxy (GFRPs) and basalt fiber/epoxy (BFRPs) composites manufactured using vacuum-assisted resin infusion molding (VARIM). The tensile and fatigue tests are performed, and results show that both GFRPs and BFRPs have very similar tensile behavior, whereas BFRPs perform better than the GFRPs in terms of fatigue life and degradation of properties, showing about 75 MPa more fatigue limit. The S-N curve shows that BFRPs resist fatigue failure and stiffness degradation due to their better interfacial adhesion. Fractographic observations reveal fatigue failure mechanisms of both BFRPs and GFRPs. From the regression analysis performed, an S-N curve was fitted with a model available in the literature, and regression parameters were calculated. Dynamic mechanical analysis of both BFRPs and GFRPs was performed to evaluate parameters like glass transition temperature, storage modulus, and loss modulus. From the findings of this research, BFRPs may be recommended as a suitable alternative to GFRPs. Highlights • This article compares the tension-tension fatigue properties of unidirectional GFRPs and BFRPs. • From the research work, the authors found that BFRPs perform better than GFRPs under fatigue loading. • The stiffness degradation behavior of GFRPs and BFRPs are studied and compared. • Scanning electron micrographs of fractured samples are used to observe fatigue failure mechanisms. • Dynamic mechanical analysis (DMA) was performed to determine the storage modulus, loss modulus, glass transition temperature, and damping coefficient (tand) for both composites. [ABSTRACT FROM AUTHOR]

Glass Fiber Reinforce Polymer (GFRP) composite Joints were studied under monotonic loads for aerospace and marine applications, but cyclic loading is also a common and serious concern in these applications. In this current study, GFRP composite pin joints were analyzed under cyclic loading, at various geometric factors experimentally and numerically using finite element analysis (FEA) and also compared with monotonic loading. Fatigue tests were carried out using sinusoidal tension-tension loading and covering a range of stress levels from 50% to 90% of effective failure strength (EFS). Weibull distribution was utilized to predict the reliable fatigue life of joints at various joint configurations. Under cyclic loading rapid degradation of dynamic modulus indicated catastrophic failure with shorter fatigue life, while gradual degradation implied slow micro-crack growth and extended fatigue life with progressive failure while in monotonic loading, a sudden fall in the stress-strain curve represented catastrophic failure, and a zigzag curve indicated bearing failure mode before fracture. The damage rate was also determined from the hysteresis loop cycles which indicate greater loop expansion due to the stiffness degradation and higher energy dissipation shows rapid damage accumulation and shorter fatigue life at higher stress level. On the other hand at lower stress level, moderate enlargement of the hysteresis loop demonstrates extended fatigue life with slower damage propagation. [ABSTRACT FROM AUTHOR]

The use of an open-graded friction course (OGFC) as a road surface demonstrates significant advantages in reducing driving noise and improving road drainage and safety. This study aims to enhance the overall performance of OGFC-13 by incorporating double-adding fiber technology. Laboratory tests were conducted on six OGFC-13 mixes modified with varying fiber ratios of lignin fibers (LFs) and glass fibers (GFs). Both GF and LF significantly improved high-temperature performance, with dynamic stability values increasing proportionally to GF content. The LF:GF = 0.15:0.15 ratio achieved peak shearing strength, demonstrating better improvement over single-fiber modification. Furthermore, both fibers effectively enhanced resistance to cracking, with GF-reinforced specimens excelling in bending stress and LF-reinforced specimens demonstrating the highest flexural strain. Water stability evaluations highlighted the substantial positive impact of LF and GF, with simultaneous addition resulting in superior moisture stability compared to single-fiber modifications. Anti-stripping performance assessments indicated that the LF:GF = 3:0 ratio exhibited the best performance. In fatigue performance, both LF and GF enhanced fatigue life, with GF outperforming LF. The LF:GF = 0.15:0.15 ratio achieved a balanced fatigue performance. Results from the radar evaluation method underscored a more comprehensive improvement in road performance achieved through double-adding technology. The LF:GF = 0.15:0.15 ratio emerged as the optimal choice for overall road performance. [ABSTRACT FROM AUTHOR]

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This work aims to determine how the behaviour of symmetry and asymmetry can affect the bending fatigue performance of glass-fibre-filled PA66 gears. Gears with pressure angles ranging from 20° to 35° at increment steps of 5° on the driving side and 20° on the coast side are considered. Temperature in the gear contact region was recorded at various torque levels to examine the effects of increasing torque on different polymer test gears and gear profiles. According to the findings of the fatigue test, the PA66/40GF gear demonstrated a 23% increase in fatigue life when the pressure angle on the drive side was increased from 20° to 35° and a 38% increase when a torque of 0.8 Nm was applied. When put under bending stress levels ranging from 13.11 MPa to 32.76 MPa, the performance of the PA66/40GF gear with a 20–35° gear profile was exceptional. However, for a torque of 2 Nm, this test gear was unable to withstand and cross 106 stress cycles. Along with the inclusion of glass fibre, the increased driving-side pressure angle improved the fatigue performance of polymer test gears. This leads to the conclusion that PA66/40GF is a better material for gears. [ABSTRACT FROM AUTHOR]

Conventional constant amplitude life diagrams (CLDs) model cannot reasonably describe mean stress effect and stochastic uncertainty present in the fatigue failure process of composite materials. To address this problem, taking the spatial mapping relationship between probabilistic S‐N curves and probabilistic CLD model as an entry point, a probabilistic CLD modeling method is proposed under the assumption of linear equations and the assumption of equiprobable quantile point between static strength distributions and fatigue life distributions. The p‐S‐N curve is established using fatigue test data from different load zones divided by different stress ratios. Subsequently, the p‐CLD model is derived through the spatial mapping relationship of the p‐S‐N curve. The method is validated by fatigue test data of glass fiber/polyester resin composites. The results indicate that the proposed method can offer an accurate description of the probabilistic behavior of composite materials. [ABSTRACT FROM AUTHOR]

Given the time-consuming and complex nature associated with the aging of composites, a novel fabric pre-aging method was developed and evaluated for static and fatigue testing. It allows for investigating sizing and interphase-related aging effects. This fast method is independent of the diffusion processes and the composites' thickness. Moreover, the new methodology offers enhanced analysis of the sizing, interphase, and fiber-related degradation of composites without aging them by conventional accelerated procedures or under severe maritime environments. For validation purposes, fiber bundle, longitudinal, and transverse tensile tests were performed with five different glass fiber inputs. Significant differences in the durability of composites were found for pre-aging and classical aging, respectively. The impacts of degradation of the single constituents on the fatigue life are identified by cyclic testing of untreated, pre-aged, and wet-aged composites. Here, it is evident that the interphase strength is likewise essential for the tension-tension fatigue performance of unidirectional composites, as is the fiber strength itself. In summary, the presented method provides industry and academia with an additional opportunity to examine the durability of different fibers, sizings, and composites for design purposes following a reasonable methodology. [ABSTRACT FROM AUTHOR]

In this present study, a high‐performance structural epoxy biocomposite has been prepared and characterized for its mechanical, wear, and fatigue behavior. The main aim of this research was to determine the effect of fiber stacking order and the biosilica addition in the epoxy hybrid composite when it is subjected to external loading. The research also focused on how the surface treatment process on fiber and particle affects the mechanical, wear, and fatigue behavior of composite. The biosilica particles were synthesized from black rice husks and then surface treated with 3‐aminopropyltriethoxysilane. Similarly, a base treatment was applied to fiber mats and the composite laminates for this investigation were fabricated by hand layup process. It is noted that the composite designations E12 and E22 exhibited an improved tensile strength of 58, 62% and flexural strength of 45, 51% for 1.0 vol% biosilica in both staking sequence models. Similarly, in inter‐laminar shear strength the composites E2, E21 and E22 outperformed than E1, E11, and E12. In terms of Izod impact toughness and hardness, composite designation E22 provides maximum increment of about 94% and 5%. The wear resistance of composite E22 exhibited lower wear loss and COF. The highest fatigue life count of 41,782 was observed for the composite designation E22 in tension‐tension fatigue mode. Overall the stacking order R/A/G/A/R gives better results than others. These load bearing properties enhanced hybrid composites might be employed in structural, industrial, automotive, home appliance, defense, and lightweight industrial applications. [ABSTRACT FROM AUTHOR]

Composite materials have seen a substantial increase in use in aerospace, aircraft and automobile industries as a result of the high expectations on material performance raised by emerging technologies. Fatigue loads are mostly inevitable in these applications. As a consequence, in addition to static strength, current designs require fatigue analysis. Hence, in this investigation, hollow cylindrical composites, constituted by glass and carbon fibres with an epoxy matrix, were considered for evaluating their static and fatigue behaviour. These specimens were tested in load control mode using an in-house built rotating bending fatigue machine at a test frequency of 10 Hz with zero mean stress. To determine the scatter in fatigue life of the developed composite specimens and to create life distribution graphs at any probability of survival percentage, the two-parameter Weibull distribution function was used. Results indicate higher shape parameters for both the composites, at lower stress levels, which represent less dispersions in the fatigue life under high cycle fatigue. Matrix cracking, interfacial delamination, fibre pull-out, and longitudinal splitting of the matrix along fibre failures are observed using a scanning electron microscope. [ABSTRACT FROM AUTHOR]

The present study focuses on investigating the impact of hybrid composite content and loading parameters on the fatigue life of E-glass fiber-reinforced composite. A mathematical model of the fatigue life was developed based on experimentation and expressed as a function of the composite content (Epoxy content (80%, 60%) wt., Novolac content (20%, 40%) wt., E-Fiber Glass content (10%, 20%, and 30%) wt.), and different loads using Adaptive Neural Fuzzy Inference Systems (ANFIS). In order to validate the ANFIS model, 30 fatigue cycle experiments were conducted. Using the experimental data sets, the ANFIS was trained with a momentum algorithm and an average absolute percentage error of 6.045% was obtained and compared to the output of the conventional Artificial Neural Network (ANN) Model. The testing accuracy was then verified with 6 extra experimental data sets and the average predicting error was 5.18%. the predicted ANFIS output data were then used to discuss the effect of the composite content and loading parameters on the fatigue life. The number and shapes of cracks observed on the failed specimens were analyzed under an optical microscope. The analysis revealed that the loading impact showed the highest influence on fatigue life for all types of enforcement and the sequence of strength was E-glass fiber, epoxy, and Novolac contents, respectively. [ABSTRACT FROM AUTHOR]

Ultra-thin friction courses (UTFC) have demonstrated exceptional efficacy in the preventive maintenance of asphalt pavements. Despite this, research into the influence of reclaimed asphalt pavement (RAP) and glass fiber on the fracture behavior of UTFC mixtures under cyclic loading is sparse. In response, this study conducted both monotonic loading tests and tension cyclic loading tests on notched semi-circular specimens at a temperature of 25 °C to elucidate the impact of RAP and glass fiber on UTFC's fracture resistance. The findings revealed that, during monotonic testing, the introduction of RAP appeared to bolster mechanical performance by increasing peak load and tensile stiffness index (TSI). However, RAP diminished the fracture energy, with the concurrent addition of RAP and glass fiber resulting in further compromise to fracture resistance. Conversely, in the cyclic loading tests operated under load control, the integration of RAP positively influenced fatigue life. Furthermore, the addition of 0.1 % glass fiber (identified as H-25R-0.1F) also improved fatigue life, highlighting its beneficial role in augmenting fatigue endurance. When compared to the mixture devoid of RAP, the inclusion of 25 % and 50 % RAP led to substantial increases in cumulative dissipated energy by 101 % and 398 %, respectively. These results suggest that both RAP and glass fiber have nuanced effects on the fracture and fatigue properties of UTFC mixtures, with potential implications for their application in roadway construction and rehabilitation. Minimum rate of cumulative dissipated energy change (R CDEC_ min) could be used to characterize the fatigue performance. The lower the R CDEC _min , the larger the fatigue life. There existed a power law relationship between R CDEC _min and fatigue life, which was independent of the mixture type. Compared to the cumulative dissipated energy method, the maximum displacement method may be more suitable to characterize the damage evolution during the fatigue test. [ABSTRACT FROM AUTHOR]

An experimental investigation was performed in predicting the consequences of the exposure to seawater and moisture absorption on the mechanical properties of two different GFRE pipe rings made of E-glass and S-glass fiber and utilized in aircraft fuel pipe line system. Filament winded tubular composite pipe rings were immersed in seawater for two, four and six months, respectively and their moisture absorption was noted. The outcomes exhibit a remarkable decrease in fatigue life for saturated GFRE sample rings. In contrast, a water absorption up to 40% of the maximum content exhibited no impact. The tests revealed debonding and cracks in the fiber and matrix interphase in the case of samples immersed in seawater on a long-term basis, although the applied mechanical load was zero. [ABSTRACT FROM AUTHOR]

To delay the expansion of reflective cracks on semi-rigid base asphalt pavements and strengthen the cracking resistance of asphalt rubber stress-absorbing membrane interlayers, the bonding and fracture performances as well as cracking resistance of a fiber-reinforced asphalt rubber stress-absorbing membrane interlayer (FAR-SAMI), rubber asphalt stress-absorbing membrane interlayer (AR-SAMI), and SBS-modified asphalt stress-absorbing membrane interlayer (AS-SAMI) were studied. In addition, the resistance to reflective cracking for FAR-SAMI was evaluated by finite element (FE) analysis. The results show that FAR-SAMI exhibits appropriate bonding performance at 15 and 40 ° C. The addition of glass fiber increases the toughness of the composite specimens and the fracture energy of FAR-SAMI increases by 23% compared with AR-SAMI. Furthermore, FAR-SAMI is effective in restraining the development of reflection cracks and prolonging the fatigue life. FE analysis also shows that FAR-SAMI can significantly reduce the stress concentration phenomenon in the crack. Therefore, fiber-reinforced asphalt rubber was found to be suitable as a SAMI to prevent and control reflective cracking. [ABSTRACT FROM AUTHOR]

Sulfate-rich dispersive soils are worldwide responsible for damaging earthworks, such as roadway roadbeds and embankments. One of the causes for such behavior is the high amount of exchangeable sodium ions adsorbed on their clay particles vastly increasing erosion susceptibility, being responsible for problems as piping, ravines, and water turbidity. In order to reduce the erodibility, it is usual to treat such soils with calcium-based stabilizers. However, in the presence of sulfates, when combined with calcium-based stabilizers in the soil, reactions take place between stabilizers and sulfates to form expansive minerals. Namely, these minerals are known as ettringite and thaumasite and are responsible for excessive volumetric swell. In this context, the present research aims to develop alternative soil stabilizers (industrial byproducts plus artificial pozzolans) and reinforcements (fiberglass) to solve problems associated with sulfate-rich dispersive soils. Thus, a binder composed of carbide lime and ground glass was used. In addition, fiberglass was applied to look for enhanced mechanical properties of the materials. To assess the efficiency of the proposed stabilization and reinforcement, unconfined compressive and splitting tensile strength, ultrasonic pulse velocity, wet and dry durability, and fatigue life tests were carried out. Soil–ground glass–carbide lime-fiberglass blends were molded at different porosities, carbide lime, ground glass, and fiberglass contents. Results show that unconfined compressive and split tensile strength and initial shear modulus are highly dependent on changes in porosity and lime content. Durability, expressed as the accumulated loss of mass, could be assessed through the adjusted porosity/lime index (η/Liv). Fiberglass inclusion resulted in higher tensile strength. The fatigue life was correlated to the η/Liv index through a negative exponent. The greater the carbide lime level, the smaller was the fatigue life for all treated specimens. An increase in porosity results in fewer contacts between particles, whereas an increase in carbide lime content enhanced the specimen's rigidity. [ABSTRACT FROM AUTHOR]

A glass fiber-reinforced epoxy (GFRE) composite, constituted by glass fibers in off-axis directions, i.e., [± 45°]2S was considered in this investigation for evaluating its static and fatigue behaviors. During the tensile test, GFRE composites exhibited nonlinear behavior, and subsequently reaching the ultimate point, test specimens rapidly failed owing to fiber failure. Fatigue tests were conducted under completely reversed rotating bending loads. The fatigue degradation model suggested by Hwang and Han was adopted to illustrate the effect of five different stress levels and test frequency (10 Hz) on the fatigue life of GFRE composites. From the obtained results, it was evident that the fatigue degradation model suggested by Hwang and Han shows good agreement with experimental results as compared to the S–N curve and Basquin's approaches. From SEM results, matrix cracking and fiber pullout were observed at lower stress levels, whereas under higher stress levels propagation of cracks in the longitudinal direction was majorly responsible for catastrophic failure of fibers. [ABSTRACT FROM AUTHOR]

To improve the fatigue behaviour of the concrete, this paper explored a potential innovative method: the joint addition of expansive agents (EA) and glass fibres (GF). It was envisaged that the addition of EA reduced additional defects caused by the addition of GF to the concrete, while the compressive prestress caused by EA enhanced the bonding between GF and the concrete, thereby improving the fatigue behaviour of the concrete. The test results indicated that the synergistic effect of EA and GF effectively improved the static bending strength, fatigue life, and deformation performance of the concrete. The synergistic effect of EA and GF on the fatigue life of the concrete was revealed qualitatively and quantitatively. The synergistic effect was further demonstrated from perspectives of the fatigue deformation and fatigue stiffness. Furthermore, P - S - N curves of EA and GF reinforced concrete were established, and the fatigue ultimate strength and conditional fatigue ultimate strength were provided as a design basis. This paper recommended adding an appropriate amount of EA to glass fibre reinforced concrete to achieve better concrete properties. • Joint addition of EA and Gf was a potential method for improving concrete. • Bending tests were used to elucidate fatigue bending performance of concrete. • Synergistic effect of EA and GF on fatigue performance of concrete was reveal. • Using two-paramater Weibull distribution, P - S - N curves were established. [ABSTRACT FROM AUTHOR]

In the asphalt pavement with semi-rigid base, the shrinkage cracks initiating from base course often propagate upward to surface course to develops into reflective cracks. The fiberglass grid, as a woven geotextile, is widely used to retard the occurrence of reflective cracks in China, but the impacts of material composition and knitting methods of it on reflective cracks are still not clear. In this paper, two kinds of models, including a two-scale model of fiber bundle-fiberglass grids layer and a coupled thermo-mechanical model of pavement structure, are established. In the two-scale model, the elastic constants (ECs) of fiber bundle and fiberglass grids layer are calculated under different compositions and knitting methods and then assigned to the coupled thermo-mechanical model to estimate the fatigue lives at initiation phase (FL-IP) and propagation phase (FL-PP) of reflective cracks based on an estimation theory. Moreover, this study designs the laboratory tests to validate this estimation method of fatigue life. Then, based on the predicted fatigue life at different phases of crack progression, the sensitivity analysis is implemented to analyze the impacts of composition and knitting methods on the fatigue life. As a result, the recommendations on design and preparation of fiberglass grid are proposed. The results show that, in material composition, the glass fibers with high elastic modulus and volume fraction and the coating materials with high elastic modulus are beneficial to retarding the initiation and propagation of reflective cracks and in knitting methods, increasing density of fiber bundles parallel to the traffic direction and reducing braided angle also has positive effect. These results can be used to optimizing design and preparation of fiberglass grid to reduce the occurrence of reflective cracks in asphalt pavement. [Display omitted] • Two-scale model of fiberglass grids layer is developed. • A fatigue life estimation method is proposed for the crack initiation and propagation phases. • The material compositions and braid parameters of the fiberglass grid affect crack initiation and propagation. • The study presents recommendations for the design and preparation of fiberglass grid. [ABSTRACT FROM AUTHOR]

In the present study, experimental investigations have been carried out to study the effect of low cycle vibration fatigue on the dynamic characteristics of hybrid composite beams with central hole reinforced with carbon nanotubes (CNT) and compare the performance of composite beams without central hole. Neat glass fiber reinforced polymer (GFRP) and CNT hybridized GFRP composite beams (CNT-GFRP) were fabricated using vacuum-assisted hand lay-up technique. Quasi-isotropic composite beams with ply orientation of [45°/−45°/0°/90°]S were fabricated. Initially, experimental modal analysis was carried out to identify the natural frequencies of GFRP and CNT-GFRP composite beam without and with central hole under clamped-free end conditions. Then, the composite beams were exposed to vibration induced fatigue through an electrodynamic shaker at various cycles of operation nearer to their fundamental natural frequencies. The experimental modal analysis was performed on the test specimens at every stages of vibration induced fatigue cycle and the natural frequencies and damping ratios were identified. Owing to the cyclic fatigue induced on the composite beams, a reduction in stiffness of the composite beams with increase in cyclic fatigue was observed through the reduction in natural frequencies of composite beams without and with CNT reinforcement. The results also showed that the presence of CNT not only imparted a higher stiffness to the composite beams but also enhanced its resistance to the deteriorating stiffness and provided an improvement in overall life of the structure. Further, the results provide a guideline for the designer on enhancement of low cycle fatigue life of structures using CNT reinforcement. [ABSTRACT FROM AUTHOR]

In this research, static and fatigue characteristics of fibrous materials is presented. The effects of fiber orientation, pressure ratio and mean stress on the fatigue characteristic of glass fiber/reinforced epoxy are investigated via testing tubular samples with different orientations of fiber [±45°] 3s and [0°, 90°] 3s. All samples were subjected to an internal pressure at several pressure ratios and/or a reversed bending moment. The test results indicated that, [0, 90°] 3s samples had the highest bending strengths at various pressure ratios; when exposed to a minimum value of local shear stress which is zero. Pressure ratios effect is observed. It was obvious that any increase of pressure ratio had an adverse effect on samples fatigue strength for any orientation. Mean stress influence was discussed and it was stated that it had a detrimental influence on fatigue life samples with any orientation and at any pressure ratio. A new form of Goodman's equation for the present case of loading was presented and proved to be appropriate for demonstrating mean stress influence for present work. [ABSTRACT FROM AUTHOR]

Experimental studies have been conducted to evaluate static tensile and tension–tension fatigue response of unidirectional glass fiber non-crimp fabric composites subject to seven different stabilization patterns (two multiaxial and five uniaxial stabilizing yarns). The effect of stabilization patterns on non-crimp fabric is crucial as they produce different mesoscale bundle shapes and bundle volume fractions which may affect the static and fatigue properties of non-crimp fabric composites. The studies show that tensile modulus and fatigue life decline with increasing amount of uniaxial stabilizations. Different stabilizations with different bundle shapes influence the final composite properties through various factors than just the volume fraction. The multiaxial stabilizations with higher static tensile strength have shorter fatigue life as compared to uniaxial stabilizations with lower tensile strength. As the areal weight of stabilizing yarns increases, fatigue life decreases at all stress levels which show the deleterious effects of stabilizations on the fatigue behavior of composites. Areal weight and orientation of stabilizing yarns should be optimally selected for the anticipated performance of the non-crimp fabric composites. [ABSTRACT FROM AUTHOR]

This research investigation explores the dispersion effectiveness of P c (percolation threshold), 0.5, 1.0, 1.5 and 2.0 vol fraction of MWCNTs (Multiwalled Carbon Nanotubes) in epoxy using UV–Vis (Ultraviolet Visible Region) spectroscopy, their effect on the rheological properties of the solvent and mechanical properties of the fabricated NCs (nanocomposites). Addition of higher amount of MWCNTs increased the absorptivity of the solution in UV–Vis region depicting higher number of untangled and individual MWCNTs in the solution. However, post ultrasonication reagglomeration of these nanoparticles was found to be inevitable and its rate depended upon the amount of nanotubes in the epoxy. Addition of MWCNTs increased the viscosity of the polymer but they were found to be unable to diminish its shear thinning behaviour. Once proper dispersion of the nanotubes in the epoxy was confirmed by UV–Vis spectroscopy, their NCs with (three-phased) and without (two-phased) glass fibers were prepared. Tensile tests asserted that an increase in MWCNT content in the matrix increase toughness of the prepared nanocomposites. Individual CNTs contributed to the ultimate strength of the laminates and their aggregates enhanced the strain to failure. Addition of MWCNTs in GFRP (glass fiber reinforced polymer) laminates not only increased their cycles to failure but also imparted large coefficient of variation in their fatigue life. Reliability analysis and survival probability of the concerned laminates were included for their design considerations. [ABSTRACT FROM AUTHOR]

Recently, the study of hybrid nanocomposites has attracted much attention because they are highly expected for being used in many applications. In this context, there is an insisting need to investigate the effect of incorporation of silica and carbon particulates nanofillers into epoxy reinforced with woven and nonwoven tissue glass fiber. The influence of incorporation of silica (SiO2) and carbon black nanoparticles (C) with different weight fractions on the tensile properties, impact strength and fatigue performance of epoxy matrix reinforced with two types of E-glass fiber was investigated. The results showed an improvement in tensile properties, impact strength and fatigue life with addition of almost all nanoparticles contents considerably with respect to that of the neat glass fiber reinforced epoxy composites (NGFRE). Hybrid composites filled with 0.5 wt.% C exhibited the highest tensile strength and fatigue performance with an enhancement of 19% and 60% compared to NGFRE, respectively. An increase of 57% and 28% in tensile modulus and impact strength over NGFRE was obtained respectively with hybrid composites filled with 1 wt.% C. Adding 0.25 wt.% SiO2 and 0.25 wt.% C simultaneously showed an improvement in mechanical properties. SEM images of tensile and impact fracture surfaces are presented for CS 0.5 specimens which in turn reveal weak fiber/matrix interface. [ABSTRACT FROM AUTHOR]

Highlights • We reviewed the asphalt mixes modified with lignin fiber and glass fiber. • Studied of rutting, water damage, thermal and fatigue cracking in asphalt mixes. • Lignin fiber improves the resistance to low temperature cracking in asphalt mixes. • Glass fiber improves the high temperature performance in asphalt mixes. • Both fibers improve fatigue performance and water stability in asphalt mixes. Abstract Low temperature thermal cracking, rutting, moisture damage and fatigue cracking are popular damages that appear in the asphalt mixture. These problems occur mainly because of the growth in the number of heavy load vehicles, design and construction errors and environmental condition that reduce the quality, performance and the service life of the pavement. Several previous studies showed that using additives like fibers to modify asphalt mixtures could enhance the efficiency and boost the quality and service life of the pavement. This paper presents a review of the role of lignin and glass fiber as a modifier in bituminous mixes. To evaluate some main mixture properties, some tests such as the low temperature bending, indirect tensile strength, the wheel loading tracking, Hamburg wheel tracking, Marshall immersion, freezing-thaw splitting, third-point bending fatigue and indirect tensile fatigue are applied to analyze rutting, low temperature cracking resistance, moisture damage resistance and fatigue resistance of asphalt mixture modified with lignin or glass fiber. Results denoted that the quality of asphalt mixture enhanced significantly by adding lignin fiber or glass fiber. Previous researches demonstrated an obvious improvement in low temperature performance in the pavement when adding 0.2–0.4% lignin fiber of asphalt mixtures, with a limited improvement of high temperature performance. On the contrary, the asphalt mixtures modified with 0.2–0.6% glass fiber of asphalt mixtures significantly improved the resistance of high temperature. So it is hard to improve all the performances of the mixture by using only a single admixture at the same time. Thus, a new way of modifying asphalt mixture that is called double-mixture technology or composite modification, which is able to enhance the overall properties of asphalt mixture. [ABSTRACT FROM AUTHOR]

This paper presents the fatigue behavior of Glass Fiber Reinforced Polymer (GFRP) composites at constant amplitude tension-tension loading conditions. A two parameter residual strength and fatigue life model has been proposed by accounting the effect of stress ratio when the structure undergoes continuous loading. A model is also developed to predict the fatigue life of GFRP composites based on fatigue endurance limit. Experiments were conducted on GFRP composite specimens to predict fatigue life and residual strength at various stress levels. Tests were also conducted to gain an understanding of the tensile behavior of GFRP composite specimens under different quasistatic strain rates. The lowest tensile strength resulting from strain rate studies has been used ultimately for conducting fatigue life and residual strength tests. Reliability of the proposed models has been verified with experimental results and with the models seen in literature. [ABSTRACT FROM AUTHOR]

A comprehensive fatigue characterization of Glass Fiber Reinforced Plastic (GFRP) and composite sandwich panels under random ocean current loadings is presented in this paper. Two sources of randomness in ocean currents were considered in the calculation of fatigue load: one is turbulence in the ocean currents and the other is the wake flow behind the support structure of the turbine. Calculated random loading was applied to conduct fatigue tests on GFRP and composite sandwich coupons using a materials testing machine. Fatigue life of GFRP coupons followed a power function pattern with respect to number of spectrum passes, while that of sandwich panels was linear in semi-log scale. The failure modes, S-N curve, and the constant life diagram under constant amplitude test are also discussed. [ABSTRACT FROM AUTHOR]

This paper deals with the influence of buckles, a mesoscopic out-of-plane defect, on the fatigue behavior of a GFRP. Three cases were investigated: samples with no defect and two kinds of samples with buckle defects generated in the longitudinal or the transverse direction. Firstly, static tests were used to measure the differences in the mechanical properties of the two defect orientations and determine where the areas of maximum local strain were located. Secondly, fatigue tests were performed in the three configurations. The results revealed that both defect orientations have a significant effect on the fatigue behavior. The configuration with defects in the transverse direction was the most crippling condition but the longitudinal configuration was also strongly affected by the presence of mesoscopic defects. It was concluded that this mesoscopic out-of-plane defect has a major negative influence on the fatigue life of such a composite. [ABSTRACT FROM AUTHOR]

The fatigue performance of laminated glass fiber reinforced polyamide composites was investigated in this study. Fatigue tests were conducted on both unidirectional and cross-ply specimens at room temperature. The S-N diagram of [0] 8 followed a bilinear curve, however, the [90] 8 laminates presented a linear S-N diagram. Compared to the same lamination of glass/epoxy, [0] 8 and [90] 8 glass/polyamide laminates presented a lower fatigue resistance, while [0 2 /90 2 ] s laminates exhibited a superior fatigue resistance. In addition, stiffness degradation was investigated for the laminates and was compared with that of glass/epoxy with the same lamination. Glass/polyamide composites had lower stiffness reduction compared to glass/epoxy. During fatigue tests, an infrared (IR) camera was also used to monitor the temperature rise in [0 2 /90 2 ] s and [0 4 /90 4 ] s laminates resulting from mechanical cyclic loading, and to capture the temperature profile associated with the failure area in the specimens. The maximum temperature in [0 4 /90 4 ] s laminates was comparable to that of [0 2 /90 2 ] s laminates and the final temperature in some of the cross-ply specimens reached 50 °C, which was near the glass transition temperature of the polyamide matrix. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive experimental investigation on the fatigue response of glass-filled epoxy composites when subjected to cyclic loading. Rod-shaped particulate glass fibers in a volume fraction of 0%, 5%, 10% and 15% are reinforced in the epoxy matrix. The mechanical behavior of the resulting composite is studied under monotonic tensile loading and tension–tension cyclic fatigue loading. The undergoing damage mechanisms leading to the crack initiation and its propagation are studied using the in-situ low cycle fatigue testing. The crack initiation behavior and the crack initiation life are found to be affected by different crack initiation sites such as the epoxy-fiber interface, the matrix and the fiber itself. Fractography reveals that the crack coalescence, crack propagation and the failure are largely affected by the varying volume fraction of glass fibers. The specimen with 10% volume fraction is found to exhibit the maximum fatigue life under the applied cyclic loading. • Rod-shaped glass fibers in varying volume fraction are used in the epoxy matrix. • Composites are subjected to monotonic and cyclic tension–tension loading. • Epoxy, the fiber and their interface are identified as the crack initiation sites. • Fibers act as crack nucleation sites resulting in coalescing the microcracks at the interface. • The specimen with 10% volume fraction exhibited the maximum fatigue life. [ABSTRACT FROM AUTHOR]

Bio-based bacterial cellulose (BC) epoxy composites were manufactured and their mechanical properties were examined. The BC was initially fabricated from Vietnamese nata de coco by means of alkaline pretreatment followed by solvent exchange. The obtained fibers were dispersed in epoxy resin (EP) by both mechanical stirring and ultrasonic techniques. The resulting blend was used as the matrix for glass-fiber (GF) composite fabrication using a prepreg method followed by multiple hot-press-curing steps. The morphology, mechanical characteristics and mode-I interlaminar fracture toughness of the fabricated composites were investigated. With a 0.3-wt% BC content, the mode-I interlaminar fracture toughness for both crack initiation and crack propagation were improved by 128.8% and 1110%, respectively. The fatigue life was dramatically extended by a factor of 12, relative to the unmodified composite. Scanning electron microscopy images revealed that the BC plays a vital role in increasing the interlaminar fracture toughness of a GF/EP composite via the mechanisms of crack reflection, debonding and fiber-bridging. [ABSTRACT FROM AUTHOR]

The fatigue lifetime of composite pipe subjected to cyclic internal hydrostatic pressure with variable amplitudes is considered. Progressive damage modeling technique is utilized on the basis of stiffness degradation for monitoring damage progress in composite structure. The modeling which consists of three different phases as stress analysis, damage estimation and mechanical properties degradation is implemented in parallel with the random generation of fatigue loading pattern. All involved parameters defining the fatigue loading scheme, including maximum stress amplitude, mean stress amplitude and number of cycles are treated as random variables resembling real conditions of pipes in the operational field. Therefore, instead of deterministic fatigue analysis as a normal practice regulated by normative standards for the experimental analysis, full stochastic fatigue modeling is conducted. Obtained results are statistically analyzed and the probability of each estimated fatigue lifetime is reported. [ABSTRACT FROM AUTHOR]

• Hydrolysis leads to homogeneous degradation, oxidation to heterogeneous degradation. • PA 6,6 fatigue life is significantly decreased during hydrolysis or oxidation. • In the homogeneous case, a flory approach links loss in fatigue to molar mass. • A bilayer model is used to quantify the decrease in fatigue life due to oxidation. In this study, the effect of hydrolysis and oxidation on fatigue life of Polyamide 6,6 reinforced with 30 wt% glass fibers has been studied systematically for the first time. The chemical changes due to these two chemical processes were monitored, especially the molar mass decrease over ageing time, homogeneous throughout the sample for hydrolysis and localized in a near-surface layer for oxidized samples. In both cases the fatigue life was significantly decreased with ageing. For homogeneously aged samples, the maximal applied stress at a given number of cycles to failure was correlated to the decrease of the molar mass of the matrix using a Flory-based model. This leads to the definition of a critical molar mass around 13 kg/mol which can be linked to the molar mass between entanglements, suggesting that fatigue is governed by fracture occurring in the glassy amorphous phase. To explain the decrease in fatigue life for oxidized heterogeneous samples, we proposed that a brittle layer, smaller than the oxidized layer itself, is considered as not sustaining any stress. The existence of this brittle layer was confirmed by fracture surface analysis and found in good agreement with the values extracted from the analytical model proposed. [ABSTRACT FROM AUTHOR]

Steel plate connection is popular in modern timber structures. However, the steel plate may be subjected to corrosion issue due to the presence of moisture in timbers. This paper proposes to replace steel plate with glass fiber reinforced polymer (GFRP) plate for connecting timber elements, so that the durability of the timber structure is expected to be improved. An experimental study is presented on the static and fatigue performances of the proposed GFRP-timber bolted connections. Variables including bolt diameter, number of bolt rows, number of bolt columns were selected to understand their effects on the static and fatigue behaviours of the connections. Failure modes, load–displacement curves, static bearing capacities, fatigue lives, stiffness degradations of the GFRP-timber bolted connections were reported. The residue bearing capacities of the connections were tested after the fatigue loading tests to assess the fatigue effect on the connection static behaviour. This study contributes to the understanding of the mechanical behaviour of GFRP-timber bolted connections. [ABSTRACT FROM AUTHOR]

The interest in repair technologies for polymer composites has increased significantly over the last decades, due to the growing use of these materials in structural applications. In this study, poly (ethylene-co-methacrylic acid) (EMAA) was used as self-healing agent to glass fiber/epoxy composite. Materials with EMAA contents of 2 wt% and 5 wt% were manufactured using Resin Transfer Molding (RTM) and the effects of the healing agent on the properties were investigated using tensile tests and Dynamic Mechanical Analysis (DMA). Results show slight variation of properties, which was more pronounced as the content of EMAA increased. In addition, the healing efficiency was investigated through fatigue tests and the addition of higher content of EMAA increased the number of cycles to failure after the healing activation cycle. • EMAA as self-healing agent for glass fiber/epoxy composites. • S–N curves were built for composites with two different contents of healing agent. • EMAA affected fatigue life of self-healing composites depending on particle content. • Healing is more efficient when activated in early stages of damage. [ABSTRACT FROM AUTHOR]

This study concerns the multiaxial static and fatigue strength properties. Short-glass-fibre-reinforced phenolic-resin composites (SGP) molded by injection and compression processes were subjected to tensiontorsion combined static and fatigue tests at room temperature under various test conditions. Tension - torsion combined static strength well agreed with Tsai-Hill failure criteria without depending on processes. Relationships between the maximum principal stress, σp1, max, and the number of fracture cycles, Nf, were approximately linear in the whole range of up to 106 cycles. For a unified evaluation of multiaxial fatigue life for SGP, non-dimensional effective stress, σ*, defined by modifying Tsai-Hill failure criteria was applied. The slopes of σ*- Nf curves according to Baskin's law were almost identical to the injection (n = 26.3) and compression (n = 26.2). We finally confirmed that the multiaxial fatigue life of SFRP could be predicted by using σ* with a unique Wöhler curve without relying on molding processes. [ABSTRACT FROM AUTHOR]

Effect of moisture conditions on the fatigue lives of woven glass-fibre-reinforced polyamide 6,6 composite was investigated. Fatigue tests were conducted at a stress ratio of R = 0.1 on specimens of different stacking sequences, namely [(0/90) 3 ], [(90/0) 3 ] and [(± 45) 3 ] and different moisture contents (RH0, RH50 and RH100). Although moisture content highly affects the fatigue life for high stress levels, this effect tends to lessen for lower stress levels. As this phenomenon was unexpected, additional fatigue tests in climatic chamber were performed. These tests support initial results and confirm the fact that the effect of moisture tend to decrease for low stress levels. In addition, this study proposes an enhanced fatigue life model to predict accurately the fatigue lives of this material for any moisture content and fibre orientation. This model shows a good correlation with experimental data. [ABSTRACT FROM AUTHOR]

Tensile strength was measured on 30 wt% glass fiber-reinforced postconsumer waste and postindustrial waste recycled nylon blends. Fatigue tests were performed under load control at a stress ratio of 0.1 at temperatures of 24 and 120°C. It was found that increasing temperature led to a significant decrease in both tensile strength and fatigue life. For unwelded postindustrial waste/postconsumer waste blends, the endurance ratio was approximately 50% regardless of the temperature. For welded postindustrial waste/postconsumer, a similar endurance ratio was observed at room temperature, but it decreased to 33% at 120°C due to the presence of polypropylene found in the postconsumer component. [ABSTRACT FROM PUBLISHER]

• The change in this modulus can be an indicator of fatigue in anisotropic materials such as composites. • No papers, that would characterize the change of elastic modulus of composites in cyclic bending and torsion. • The decrease in the shear modulus of transverse elasticity is greater, the larger the amplitude of the shear strain is applied. • The larger the amplitude of normal strain (in bending), the faster the decrease in bending moment occurs. The paper emphasizes the fact that in the case of composite materials which are characterized by anisotropy, unlike classic isotropic materials, the modulus of elasticity changes its value when the degree of damage changes. Moreover, a decrease in this modulus can characterize the degree of material damage. The literature on this phenomenon was analyzed. However, the vast majority of studies leading to the description of changes in the stiffness of the material have so far been carried out only for uniaxial tension–compression. One case was also found where the authors performed a similar analysis for the material subjected to torsion. It was found that such analysis has not yet been performed for pendulum bending, which is a very common type of load in structural elements. Based on the authors' own experimental research for cyclic pendulum bending and double-sided torsion of specimens made of polyamide PA6, reinforced with continuous glass fibers, it was found that, as in the case of uniaxial tension–compression, as the degree of damage increases, there is also a decrease in both Young's modulus for bending and the shear modulus for torsion. [ABSTRACT FROM AUTHOR]

In this paper, a macro phenomenological fatigue model is developed for the off-axis fatigue behavior of glass fiber reinforced polymer (GFRP) composite laminates. The residual stiffness method and strain failure criterion are used to characterize the brittle nature of fatigue damage evolution. This allows one to obtain a practical form of multiaxial fatigue model that takes into account of the non-linear effects of fiber orientation dependence, stress ratio dependence as well as the effect of loading frequency on the fatigue behavior of composite laminates. Parameters of the model are fitted out according to relative fatigue experiment data with specific lay-up under certain stress ratio and loading frequency. Fatigue life predictions are verified by different stress ratios and loading frequencies, and the results of the model show a good agreement with experimental data. [ABSTRACT FROM AUTHOR]

The main objective of the present work is to investigate the capability of experimental modal analysis as a nondestructive tool to characterize and quantify the fatigue behavior of laminated composite beam with different lamina orientations and cantilevered boundary condition. In the present work, experimental modal analysis was conducted on the specimens previously subjected to fatigue loading to determine the modal parameters (natural frequency, damping ratio and mode shape). This was achieved through studying the response of modal testing with different specimens of different lamina orientations as a main factor affecting fatigue life. This correlates modal parameters such as: damping ratio, natural frequency and mode shape to fatigue behavior. The composite material used in experiments is glass fiber reinforced polyester (GFRP) laminate. Plane bending fatigue tests were performed on standard fatigue specimens. The fatigue test was interrupted at different fatigue life ratios ( n / N f ) and modal testing was conducted to determine the change in modal parameters. The results showed that the changes of modal parameters provide a proper means for predicting the fatigue behavior of composite structures. From the experimental results of both dynamic and fatigue tests, curve fitting technique was used to correlate modal parameters to fatigue life. An exponential and quadratic equations have been obtained which correlate fatigue life ratio to damping ratio and resonant frequency respectively. It was noticed from the curves representing exponential and quadratic equations that the value of damping ratio ξ is more noticeable than the value of frequency, which means that the extent of fatigue damage determines the damping ratio, hence damping ratio could be said to be a good indicator of the fatigue life ratio. [ABSTRACT FROM AUTHOR]

Although the use of glass fiber-reinforced polymer (GFRP) reinforcing bars is gaining acceptance as an alternative to conventional steel reinforcement in concrete structures, little empirical data exist on the long-term fatigue performance of GFRP bars in concrete. Abrasion at the bar-concrete interface is known to have an adverse effect on bonds and on the overall member response under cyclic loading, although this effect was not adequately quantified until now. This paper presents the results of an experimental study comparing the fatigue performance of GFRP bars in air with the behavior of similar bars embedded in concrete. The experimental findings showed that the GFRP bars tested in air survived fatigue lives that were approximately a full order of magnitude longer than similar bars in concrete beams. The results were used to calibrate a statistical fatigue life model and a residual stiffness model for GFRP bars in reinforced concrete flexural members. [ABSTRACT FROM AUTHOR]

The aim of this study was to characterize the mechanical behavior of a carbon-glass/epoxy hybrid composite under cyclic loading and following physical-based interpretation for mode I delamination modeling. The hybrid composite shows a higher surface roughness due to a micro-change in the crack direction at the carbon/epoxy and glass/epoxy interfaces, with the simultaneous presence of both reinforcements along the entire fracture surface. The organosilane bond (at the glass fiber surface) extends the interphase chain, increasing the deformation interfacial area. In conclusion, the application of the maximal carbon-glass/epoxy interfacial number in hybrid laminates is a feasible option to increase delamination resistance, since a greater amount of energy needs to be overcome to enable damage formation, which results in longer fatigue life. [ABSTRACT FROM AUTHOR]

Abstract: The effect of fully reversed loading (R =−1) on high cycle fatigue performance of sandwich panels composed of polyurethane foam core and Glass Fiber Reinforced Polymer (GFRP) skins is studied and compared to that of similar panels tested under fully unloaded (R =0) conditions. Fatigue life curves are established and compared based on maximum loads of 30–70% of the ultimate monotonic strength (P ult). It was shown that panels consistently fail in shear of the foam core. The fatigue life reduces significantly at R =−1, to about 10% of that at R =0. In order to achieve at least 2 million cycles – the commonly acceptable fatigue life in structural engineering – the maximum service loads should be limited to 30% and 45% of P ult, respectively, for the cases of R =−1 and R =0. It is estimated that the threshold loading levels at infinite fatigue life are 23% and 37% of P ult, for the cases of R =−1 and R =0, respectively. By the end of fatigue life, up to 25% reduction in stiffness occurs. The transition between high and low cycle fatigue occurs between 200 and 5000 cycles. A 3-D Haigh diagram is also established for design purposes. [Copyright &y& Elsevier]

The paper presents the results of an investigation conducted to assess the fatigue-life and prediction of flexural fatigue strength of polymer concrete composites based on epoxy resin as binder material. Three point flexural fatigue tests were conducted on polymer concrete specimens using MTS servo controlled actuator, to obtain the fatigue lives of the composites at different stress levels. One hundred and thirty-seven specimens of size 40 x 40 x 160 mm were tested in flexural fatigue. Forty-three static flexural tests were also conducted to facilitate fatigue testing. It has been observed that the probabilistic distribution of fatigue-life of polymer concrete composite (PCC) and glass fibre reinforced polymer concrete composite (GFRPCC), at a particular stress level, approximately follows the two-parameter Weibull distribution, with statistical corelation coefficient values exceeding 0.90. The fatigue strength prediction model, representing S-N relationship, has been examined and the material coefficients have been obtained for GFRPCC containing 0.5% and 1.0% glass fibres. Design fatigue lives for GFRPCC containing different contents of glass fibres have been estimated for acceptable probabilities of failure and compared with those of PCC. [ABSTRACT FROM AUTHOR]

• The fatigue life of hybrid rod was significantly improved by the fiber uniformly dispersed mode. • The fatigue damage of hybrid rod was dependent on the fiber hybrid mode and stress level. • The positive hybrid effect of fatigue performance was realized to obtain the higher fatigue performances. • The fatigue life model of hybrid rod was proposed to predict the fatigue limit. In order to promote the application of fiber reinforced polymer (FRP) rod in bridge engineering, the carbon/glass fiber uniformly dispersed hybrid (UDH) rod with a diameter of 22 mm was developed as the bridge cable through the pultrusion technology. In the present paper, the tension–tension fatigue performances of hybrid rod were investigated with three stress levels of 0.33, 0.44, 0.60 and the fixed stress ratio of 0.4. The fatigue life, stiffness degradation and stress redistribution during the fatigue loading were obtained by linear variable differential transformer (LVDT) and digital image correlation (DIC) method. Furthermore, the fatigue failure mechanism was revealed by microstructure damage analysis. Through the fiber uniformly hybrid technology, the fatigue failure mode of hybrid rod transferred from shell-core debonding to uniformly carbon and glass fiber/resin interface splitting. The positive hybrid effect of fatigue performance was realized to obtain higher fatigue life, stiffness retention and residual mechanical properties. The reliable fatigue life prediction model was developed, and the recommended fatigue limit of present hybrid rod applied for bridge cable was 0.45 at the stress ratio of 0.4 to obtain more than two million fatigue cycles. [ABSTRACT FROM AUTHOR]

Aeroelastic design and fatigue analysis of large utility-scale wind turbine blades have been performed to investigate the applicability of different types of materials in a fatigue environment. The blade designs used in the study are developed according to an iterative numerical design process for realistic wind turbine blades, and the software tool FAST is used for advanced aero-servo-elastic simulations. Elementary beam theory is used to calculate strain time series from these simulations, and the material fatigue is evaluated using established methods. Following wind turbine design standards, the fatigue evaluation is based on a turbulent wind load case. Fatigue damage is estimated based on 100% availability and a site-specific annual wind distribution. Rainflow cycle counting and Miner's sum for cumulative damage prediction is used together with constant life diagrams tailored to actual material S-N data. Material properties are based on 95% survival probability, 95% confidence level, and additional material safety factors to maintain conservative results. Fatigue performance is first evaluated for a baseline blade design of the 10MW NOWITECH reference wind turbine. Results show that blade damage is dominated by tensile stresses due to poorer tensile fatigue characteristics of the shell glass fiber material. The interaction between turbulent wind and gravitational fluctuations is demonstrated to greatly influence the damage. The need for relevant S-N data to reliably predict fatigue damage accumulation and to avoid nonconservative conclusions is demonstrated. State-of-art wind turbine blade trends are discussed and different design varieties of the baseline blade are analyzed in a parametric study focusing on fatigue performance and material costs. It is observed that higher performance material is more favorable in the spar-cap construction of large blades which are designed for lower wind speeds. [ABSTRACT FROM AUTHOR]