جستجوی مقالات مرتبط با کلیدواژه « خستگی » در نشریات گروه « فنی و مهندسی »

Porous asphalt mixture is a type of asphalt mixture with good drainage. However, it has poor tensile performance and durability. Crushed basalt fibers (CBF) have been proven to be an effective additive to improve the mechanical performance and fatigue of asphalt mixtures, but little attention has been paid to porous asphalt mixtures. In this research, the effect of crushed basalt fibers with different lengths (non-fibers, 3 mm, 6 mm, 9 mm and 12 mm) and contents (3% and 4%) on the performance of porous asphalt mixture is investigated. A series of tests were performed to determine the optimal fiber length and percentage, including the shedding test, the canta abrasion test, the freeze-thaw split tensile test, the wheel groove test, the low temperature cracking resistance test, and the four-point bending beam test. After that, indirect tensile tests were conducted at different temperatures to investigate the tensile strength properties of porous asphalt mixtures with optimal fiber length and percentage. The results show that the addition of crushed basalt fibers can generally improve the performance of the porous asphalt mixture because the crushed basalt fibers form a three-dimensional network structure in the porous asphalt mixture.

This research was conducted to evaluate the performance of asphalt mixture modified with environmentally friendly calcium sulfate fiber 1 (CSWF) as a sustainable pavement material. The asphalt mixture containing 0.2% by weight, 0.4% by weight, 0.6% by weight and 0.8% by weight of CSWF was designed by Marshall's method. Asphalt mixtures without fibers were also prepared as control samples.    Marshall test, wheel rut test, low temperature bending test, moisture sensitivity test and fatigue test were conducted to evaluate the performance of CSWF asphalt mixture and the fiber reinforcement mechanism was discussed.    The results showed that CSWF can improve high temperature stability and low temperature cracking resistance of asphalt mixture. Moisture resistance of asphalt mixtures was also improved in the presence of CSWF. When the percentage of CSWF was 0.4% by weight of the total mixture, the asphalt mixture performance is the best. Compared with conventional asphalt mixture, CSWF asphalt mixture not only used power plant waste effectively to preserve ecosystems, but also improved pavement performance, which is suggested to be used in sustainable pavement construction and rehabilitation.

Bitumen aging is one of the factors causing and spreading cracks and moisture damage in asphalt pavements. Aging can occur during the production, transportation, and construction stages (short-term aging) or the operation period (long-term aging) and can cause bitumen to harden. Today, various methods are defined to simulate short-term and long-term aging. In this study, the effect of long-term aging of AASHTO R30 (as the most common standard method) and NCHRP 9-54 (as the latest method) on the fatigue performance of asphalt mixtures was investigated at strain levels of 500 and 1000 microstrains, loading frequencies of 5,10,15, and 25 Hz and temperature of 200c using a 4-point bending beam test. The results showed that both aging methods increased the initial stiffness and decreased the fatigue life of the samples at the strain levels and loading frequencies tested. Also, by comparing the fatigue life of the tested samples, it was found that the greatest reduction in fatigue life was related to the aged samples by the AASHTO R30 aging method. According to these results, it can be said that AASHTO  R30 is a conservative method in comparison with NCHRP 9-54.

Every year, huge costs are spent on the maintenance of road pavements due to premature reflective deterioration of the road surface, a large part of which is related to road surface paving. Accordingly, in order to prevent the propagation of reflective cracks in newly coated pavements, various methods have been used and researched. The results have shown that all the adopted reflective crack control methods have only delayed the propagation of this type of crack. However, some methods have caused a greater impact on the appearance of reflective cracks and reducing the intensity of these cracks, and one of the best methods is the use of geosynthetic products and interlayers. In this research, the performance of 2 different types of geocomposite (with tensile strengths of 50 and 100 kN/m) in asphalt pavements in delaying the initiation of reflective cracks compared to control samples at different temperatures and loading frequencies was investigated. Based on the studies, it was observed that the use of type I geocomposite with high tensile strength is the most effective in increasing the fatigue life and among the mentioned factors, the temperature parameter will have the most negative effect on this performance. After the temperature, in order of the type of geocomposite used in terms of tensile strength and then the loading intensity, they will have the greatest effect on the fatigue life changes (about 53,000 cycles of loading difference, between the temperature of 40 and 0 degrees Celsius) on the reinforced asphalt coatings. Based on the results of variance analysis of the fatigue life model obtained in this research, the value of R² and Adjusted R² are equal to 0.987 and 0.981, respectively, which indicates the high accuracy of the presented model.

Dissemination of polymeric waste in the environment is one of the most important concerns of the world today. Used plastics and worn tires are one of the most important sources of this type of waste. Chemically, these materials are very similar to bitumen as the most used and expensive component of asphalt mixtures. Therefore, using these waste materials as an additive in bitumen while reducing environmental pollution can improve the performance characteristics of the pavement. Investigating the effect of each type of additive on the fatigue performance of asphalt mixture is essential as one of the most important factors in causing pavement damage. Therefore, in this research, in addition to examining the physical properties of bitumen, the fatigue performance of asphalt mixture containing different percentages of waste plastic and rubber powder has been investigated using the four-point bending beam method. The results of this test using the hardness method, Normalized hardness and energy method were analyzed. The results showed that waste plastic reduced the fatigue resistance of the asphalt mixture, which was compensated to a significant extent by adding rubber powder. So that the samples containing rubber powder and waste plastic at the same time had a longer fatigue life than the control sample.

In this research, by reviewing the researches and articles, waste glass powder is investigated on the performance of asphalt mixture. In the last decade, these researchers have been using crushed glass in construction programs to prevent waste glass from being used as protective supplements and reducing the environment in construction. Crushed glass has been studied for use as materials in base and sub-base pavement layers, as well as concrete. Glass is the only material that can be completely recycled. This material is prepared by melting quartz sand, soda and lime, and also glass pieces. The glass game is collected as one of the recycled components. It is non-metallic and neither can nor does it burn, so its recovery is possible. Therefore, it is used in road construction as a substitute for stone materials in asphalt pavement with warm asphalt mixture. It showed that the addition of glass powder increases the stability of the mixture, because the glass powder filler improves the Marshall Stability results for all mixtures compared to Portland cement or limestone powder fillers. The results showed that the powder from the mixture decreases against the glass. Also, the obtained results investigated the suitability of glass as filler.

Today, with the expansion of the road network and the increase in construction and maintenance costs of pavements, using additives in bitumen has become a popular method to improve asphalt performance. Various polymeric additives are widely used additives in bitumen and asphalt mixture. This paper investigates the effects of 2, 4, and 6 wt% of Styrene-Ethylene/Propylene-Styrene (SEPS) polymer on the bitumen's behavior. In this regard, linear amplitude sweep (LAS) and time sweep (TS) tests have been used to evaluate the fatigue characteristics of modified bitumen. In addition to the common method of estimating fatigue life in the LAS test, the pseudo-stress method was also used, and the results of three techniques were compared. As a result, using SEPS in bitumen reduces the fatigue life by 12% in the sample containing 2% of SEPS; however, fatigue life increased to 27.9 times greater than virgin bitumen by increasing the percentage of SEPS. The results of LAS and TS tests show a significant difference compared to each other. The LAS test is a suitable method to check the fatigue characteristics of bitumen due to the shorter test time. According to the pseudo-stress method results, the fatigue life of the samples containing 2, 4, and 6 wt% of SEPS are 0.75, 2.5, and 15.8 times greater than the virgin bitumen sample.

Central Alborz Zone (CAZ) comprises a range of industries and a high concentration population (about one-fourth of the country's population), essential to provide material resources and create the necessary infrastructure for this massive population. The CAZ has a large variety of rock formations and facies, which causes extensive expansion in rock materials and resources. One of the major materials in the CAZ is the existence of a wide variety of carbonate rocks (Elika, Dalichai, Lar, Tizkuh, Ziarat, and Kond formations). This study aims to investigate the geological and engineering geological characteristics of six carbonate formations in the CAZ and to classify carbonate rocks based on their material and their performance in asphalt mixtures. Therefore, by sampling these formations and performing various lithological and engineering geological experiments, six studied formations have been classified, and have been used to evaluate their performance in asphalt mixtures. Selected formations include Elika, Dalichai, Lar, Tizkuh, Ziarat, and Kond. The studied carbonate rocks were classified based on the lithology and performance of their asphalt mixtures in fatigue and cracking test. This classification includes the best performance to the weakest performance, respectively, including Mudstone (Elika Formation), Bioclast Grainstone (Kond Formation), Bioclast Packstone (Dalichai Formation), Bioclast Packstone (Tizkuh), Packstone-wackestone (Ziarat Formation) and Dolostone (Lar Formation).

Analysis of structural components under fatigue loading due to the complexity of the loading is one of the most challenging problems in civil and structural engineering field. In order to find the fatigue life of a structural member, the costly and time-consuming experiments must be conducted while the collected data is very scattered and cannot be used for other conditions and problems. Therefore, finding effective numerical models to analyze a member subjected to fatigue load, could reducing time and expenses while could offer a systematic and general solution in variety of conditions. In this research, using the findings of a previous experimental study, the behavior of CFRP retrofitted and unretrofitted notched steel beams under fatigue loading has been studied by finite element by numerical modeling in a commercial finite element software. In this study, 11 notched CFRP retrofitted and unretrofitted steel beams (hot-rolled W5×10 made of A36 steel) were modeled and fatigue loaded until failure with stress range between 207 and 379 MPa under frequency of 5 to 10 Hz. The results of numerical modeling were compared with the results of previous experimental study and several equations were presented to estimate the fatigue life of unretrofitted and retrofitted specimens. The normalized stiffness losses of specimens were investigated as well. The verifications showed that numerical models and extracted equations have good agreement with the experimental results.

Nanomaterials have indicated a hopeful capacity in improving the behavior of pavement. As hot mix asphalt is a viscoelastic material, several distresses were occurred during their life time. Furthermore, steel slag was used to enhance the properties of mixture because of its outstanding physical properties. This research evaluated the effect of nanoclay and Styrene Butadiene Rubber (SBR) on performance behavior of bitumen and high and intermediate temperature performance of SMA mixtures containing steel slag aggregate. Through this paper, the AC-60/70 and AC-85/100 penetration grade bitumen’s were used as base bitumen. Moreover, SBR (0%, 2%, 4%, 6%, 8% and 10% by weight of binder), and nanoclay (0%, 1%, 2%, 3%, 4%, and 5% by weight of binder) were used as a mixture modifier. For evaluating the performance behavior of bitumen, the rotational viscosity, Dynamic Shear Rheometer (DSR), and Bending Beam Rheometer (BBR), Multiple Stress Creep Recovery (MSCR), and linear Amplitude Sweep (LAS) tests were implemented. Moreover, Resilient Modulus (Mr), Indirect Tensile Strength (ITS), dynamic creep, wheel track, and Four Point Beam Fatigue (FPBF) tests were performed to investigate the performance of mixture samples. To analyze the data statistically, two-factor analysis of variance (ANOVA) is evaluated. The rheological behavior test outcomes showed that the utilization of NC/SBR additive results in an enhancement in the rutting and fatigue resistance of binders. The utilization of NC decreases the low-temperature resistance of binders, while SBR improves the bitumen’s low-temperature resistance. Storage stability test outcomes reveal that utilization of NC enhances the storage stability of binders. Also, the application of SBR leads to enhance phase separation. The MSCR test results demonstrate an enhancement in the high-performance temperature of the virgin binder at different stress levels by the addition of NC/SBR. Moreover, the utilization of NS improves the rutting strength of samples. Based on the LAS test outcomes, the utilization of NC/SBR additives improves the fatigue properties of the asphalt binder. The mixture test results reveal that using NC/SBR increases the permanent deformation resistance, MR, ITS, fracture energy, and intermediate temperature properties of specimens.

Stress cracking is an important threat to steel industries. When certain conditions are created in the environment of steel, the loading of this defect leads to intergranular cracks in the radial-axial plane. These cracks can grow under continuous adverse loading and eventually lead to rupture. A lot of research and experiments have been done in this regard. This article is a review of the combination of conditions governing steels that lead to the growth of stress cracking. Failures caused by stress cracking occur in a long period during several stages such as germination, crack growth and final failure. On the other hand, we know that stress cracking depends on environmental, metallurgical and mechanical conditions. Therefore, in this article, the purpose of investigating the loading conditions at each stage of stress cracking and the effects of repetitive stress on steels will be discussed. Also, the synergistic effects of different parameters during the entire life cycle of steels will also be discussed. The main focus of this review is to relate the loading conditions at each stage of crack propagation, which plays an important role in estimating the remaining life of steels susceptible to stress cracking. This discussion will include how cyclic loading conditions can change steel properties and contribute to the initiation of intergranular cracking. Finally, the modeling of stress crack growth will be discussed and suggestions such as failure analysis due to stress crack growth on sheets were given.

Composite laminates are advanced engineering materials that are widely used in various industries due to their unique properties. The aim of this paper is to assess the effect of electrospun nanofibers on the fracture and fatigue behavior of composite laminates and also to investigate the performance of the Finite Element Method based on the Cohesive Zone Model, in predicting the fatigue behavior of the laminates. For this purpose, standard specimens were fabricated from carbon/epoxy Prepregs interleaved with nylon 6,6 nanofibers. The specimens were then subjected to mode I static and fatigue loading conditions. The results showed that fracture toughness was doubled by adding nanofibers between composite layers. Under fatigue loading, the crack growth rate of the nanomodified specimens was less than the virgin specimens. So, the crack growth rate decreased by 8 times with interleaving the nanofibers at 0/9 =Δ G/Gc . The Cohesive zone model method was used to evaluate the efficiency of finite element in modeling the fatigue crack growth rate in virgin and nanomodified specimens. The progressive failure model was used to simulate the fatigue behavior. Consistency of finite element results with the experimental results showed that the Cohesive zone model method is a suitable tool to model the fatigue behavior of interleaved composite laminates.

In the present study, the assessment process of the reliability of the ship structure under the two factors of fatigue failure and corrosion has been expressed using structural health monitoring data. In order to use the structural health monitoring data for assessing the reliability, Bayesian inference method has been used to update the distribution of loads over the structure. The distribution and magnitude of these loads have been updated according to the results of structural health monitoring using Bayesian approach and the results have been presented. By using the reliability criterion in the design stage, the better understanding of the structure's performance during the life of the structure can be obtained according to environmental conditions. The reliability analysis of corrosion defects and fatigue shows the decrement of reliability of the structure during its life. The use of structural health monitoring method increases the reliability index and confidence for estimating the real life of the structure obtained from the analysis.

Timely diagnosis of fatigue helps to improve the quality and effectiveness of neurofeedback training. Neurofeed back training (NFT) is a method that can change brain activity by altering brain signal fluctuations and teaches individuals to produce or reproduce their brain activity patterns in order to improve performance. Neurofeedback training has been widely utilized over the recent years owing to its considerable effect on the cognitive processes. Fatigue during NFT is one of factors affecting the functioning and achievement of NFT which results in decreased learning ability. Timely diagnosis of fatigue during NFT preserves quality of NFT.Decreased learning ability reduces individuals' motivation for learning during NFT. In this paper, 12 participants` electroencephalogram signals were investigated to detect fatigue during NFT. Two training protocols named protocol 1 and 2 have been designed to improve working memory. Each protocol includes 6 participants and 10 training sessions that each session takes three 10-minute training intervals. Training features in protocol 1 are increased in power of lower2 alpha frequency band in OZ channel and permutation entropy reduction in FZ channel, while protocol 2`s training feature is increased in power of lower2 alpha frequency band in OZ channel. Occurrence of fatigue during NFT changes trend of training features. Changing of training features slope will decrease or become opposite to the goal of NFT. Therefore, examining trend of training features slope is a novel approach in detection of fatigue during NFT. During the occurrence of fatigue, in protocol 1, trend of power of lower2 alpha frequency band`s slope in the OZ channel is decreasing and the trend of entropy` s slope in the FZ channel is increasing. Consequently, the trend of score`s slope is also decreasing. Also in the protocol 2, the trend of power of lower 2 alpha frequency band`s slope in the OZ channel and score is decreasing. This shows that training features do not change in line with the neurofeedback`s goal. Fatigue was detected for 3 subjects in the protocol 1 and 1 subject in the protocol 2. Occurrence of fatigue was less in protocol 1 compared with protocol 2 since Protocol 1 `s training features are combination of frequency and non-frequency features, while the Protocol 2 `s training feature is only frequency feature. Detection of fatigue during NFT is an essential issue which contributes to increase in the effect of training and participants` performance.

Asphalt pavements are one of the most widely constituents utilized to pave highway pavement which experience various failures during their lifetime, such as rutting, fatigue and thermal cracking. Therefore it should be used to improve the bitumen performance by addition of modifiers such as polymers and Nano Clays (NC). Among the various additives used to improve the bitumen performance, Ethylene Vinyl Acetate (EVA) is one of the most useful and effective materials for paving. In this study, the rheological behavior of bitumen and rutting and fatigue behavior of mixture containing EVA/Nanoclay and EVA latex were evaluated. EVA/NC and EVA latex were made and mixed with bitumen. Results of storage stability test shown that EVA/NC-modified bitumen is steadier than EVA-latex-modified bitumen. The results of the fatigue test of the mixtures showed that the asphalt mixtures made of bitumen modified with nanocomposite are more resistant to fatigue than bitumen modified with EVA polymer. The results showed that the addition of 6% EVA/NC and 6% EVA increased the fatigue life by 43% and 20%, respectively. The results of the rutting resistance tests showed that the rutting resistance of the samples increased with the increase of EVA polymer. Also, the addition of montmorillonite increased the resistance of polymer mixtures against rutting.

Asphalt pavements are one of the most widely constituents utilized to pave highway pavement which experience various failures during their lifetime, such as rutting, fatigue and thermal cracking. Therefore it should be used to improve the bitumen performance by addition of modifiers such as polymers and NanoClays (NC). Among the various additives used to improve the bitumen performance, Ethylene Vinyl Acetate (EVA) is one of the most useful and effective materials for paving. In this study, the rheological behavior of bitumen and fatigue behavior of mixture containing EVA/Nanoclay and EVA latex were evaluated. In order to evaluate the intermediate and high temperature behavior of binder, the Linear Amplitude Sweep (LAS) test and Multiple Stress Creep Recovery (MSCR) test were implemented. EVA/NC and EVA latex were made and mixed with bitumen. Results of storage stability test shown that EVA/NC-modified bitumen is steadier than EVA-latex-modified bitumen. MSCR test results indicated that addition of EVA/NC and EVA latex to original binder led to decrease and decrease the percent recovery and non-recoverable compliance (Jnr) values, respectively. Also LAS test results show that addition of EVA/NC and EVA latex to original binder cause an enhance in fatigue behavior of binder. According to climatic regions in Iran and required PG binders, it can be concluded that binder modified with 4% EVA/NC can use in all climatic zones in Iran followed by 6% EVA/NC modified binder.

The chewing simulator is designed to perform fatigue tests and durability on a variety of dental specimens. This device, by considering the material (hard or soft) and the type of dental sample (human or animal or artificial) and by applying a specific cyclic and even static force, changes the shape of the sample microscopically and finally this periodic loading and shape change, uses the data to evaluate the fatigue and strength of the sample in the durability test. The testing process of this device will continue until the sample fails or the loading cycle is completed. At design of this device, two movement mechanisms are considered vertically and horizontally, which are responsible for chewing simulation operations, so that in both mechanisms, the movement is reciprocating, the amount and number of this movement is cyclical that is adjustable and controllable, and at the same time, considering the force measuring sensor in this device, the amount of applied force is specified and adjustable at each stage. Two specimens of teeth were placed in the machine for testing. The first priority of testing this device for the samples was their durability under the static force that was applied to the sample step by step. Also, to evaluate the function of the device in the fatigue test, dental specimens were loaded under a certain force and were affected by cyclic motion in both vertical and horizontal directions. According to studies, the refractive force of the specimens varies from 100 N to 800 N, the dental specimens, one artificial and the other natural, failed under the static force, which was in the range of 200 N, that the artificial sample was completely broken, but the natural sample was worn out and part of it was damaged. And this was a good comparison to show the strength and durability of natural teeth compared to artificial ones.