Constant Tests Research Articles

Real-time state of charge estimation for electric vehicle power batteries using optimized filter

The main focus of the battery management system is the estimation of the battery's State of Charge (SOC), which is an indicator to determine the driving range of an electric vehicle. The Extended Kalman Filter (EKF) algorithm is the most promising for SOC estimation when the system is running. The EKF state estimation algorithm is sensitive to the process noise covariance matrix Q and measurement noise covariance matrix R. Inappropriate noise covariance matrices reduce the accuracy and cause divergence in state estimation. This paper uses the Sunflower Optimization algorithm (SFO) to find the optimal values of the noise covariance matrices before applying EKF for online SOC estimation. It is clearly stated that the iterative SFO does not affect the instantaneous response of EKF in the online estimate because the SFO is only performed once to determine the optimal values. The effectiveness of the proposed identification is examined through the constant discharge rate test and dynamic driving profile. The proposed algorithm's performance indices, such as maximum error, Mean Absolute Error, Mean Square Error, and Root Mean Square Error of SOC estimation, are low compared to the trial-error method, genetic algorithm, and adaptive extended Kalman filter. Besides accuracy, the proposed method quickly converges even when the initial SOC is inaccurate. The feasibility and benefits of the proposed SFO-EKF algorithm are demonstrated by qualitative and quantitative findings on five challenging datasets. To assess the performance of the SFO-EKF for SOC estimation in constant-current discharge and extreme drive cycle situations, three public datasets and two datasheets are employed. The simulation results show that the proposed method has high accuracy and a better convergence rate in estimating SOC under static and dynamic operating conditions.

On the Orowan stress in intermetallic ODS alloys and its superposition with grain size and solid solution hardening

Abstract The intermetallic trialuminide Al67Ti25Cr8 was strengthened by nano-scaled dispersions of up to 3 vol.% yttrium and aluminum oxide via mechanical milling. Subsequent powder consolidation, heat treatment, and thermo-mechani-cal treatment yielded grain growth to an increasing degree, resulting in grain sizes ranging from sub-μm level to about 0.5 mm. Consequently, the room-temperature yield strength σ 0 as determined by constant compression rate tests, increases due to three different hardening contributions, namely dispersion strengthening σ OR due to Orowan bypassing, fine-grain strengthening σ HP due to Hall-Petch relation, and, finally, as virtually always present, some solid-solution strengthening σ s. The analysis of the particle parameters was done using TEM as well as focused ion beam (FIB) imaging. The latter provides the opportunity to directly determine the mean radius r s of planar intersections with spherical particles and their nearest-neighbour spacing L since it displays a plane section through the 3-dimensional arrangement of dispersoids. The analysis of the strengthening contributions indicates that a Pythagorean superposition permits an appropriate modeling of the measured yield strength σ 0.

Assessment of Tube Well Pumping Test Performance on Different Geological Formation

Water supply-demand is increasing in line with the increment in population. Natural water resources are declining due to reduction of water catchment areas, river pollution and drought. This causes the raw water quantity and quality to decrease and increase water treatment costs. Groundwater usage may be able to solve this problem due to its less polluted nature which requires less treatment. The groundwater is preserved in aquifer within the geological formations, i.e., in the alluvium and fractured-rock. However, the groundwater yield of each formation is unknown unless tube well is constructed and pumping test are performed. This study aim to evaluate the tube well performance via pumping test on two different geological formations. This research focuses on the effect of transmissivity, hydraulic conductivity, and efficiency of the aquifer, which are step-drawdown test, constant-rate test and recovery test in tube well in geological formation of alluvium and fractured rock. Three well-pumping tests at each formation were conducted at IBS Universiti Malaysia Kelantan (UMK), Kelantan, Sekolah Kebangsaan Chantum, Kelantan, Sekolah Menengah Kebangsaan Agama Tok Bachok, Kelantan, FRU Wakaf Tapai, Terengganu, Kampung Dada Kering, Kuala Lipis, Pahang, and Kampung Seri Gunung Pulai, Johor, respectively. The aquifer efficiency obtained from the relationship between transmissivity and hydraulic conductivity. The suggested value of 75% efficiency is selected to present the well’s efficiency. The wells efficiency indicate that the alluvium formation has roughly uniform output between 9.39m3/h, 11.23m3/h and 23.38m3/h. Meanwhile in the fractured rock formation the efficiency was highly varied between sites, the highest is 32.33m3/h and the other two sites obtained has low output of 3.44 m3/h and 1.00m3/h respectively. The alluvium aquifer showed uniform water production compared to fractured hard rock aquifer. Meanwhile the water quantity in the fractured hard rock formation is unpredicted, which subjected to the fractured rock characteristic.

Attribute analyses of acoustic emissions in hydraulic fracturing

Hydraulic fracturing (HF) and horizontal drilling are essential to the development of shale gas and oil. Production depends on the stimulation success. During fracture initiation, propagation, and closure, cracks emit acoustic waves; these can be monitored in real time as microseismics in the field and as acoustic emissions (AEs) in the laboratory. AEs are the laboratory equivalent of field-scale microseismics and contain detailed information about HF fracture mechanics. The number of acoustic events correlates with the number of induced fractures and hence the stimulation volume. Three HF protocols under dry conditions were carried out on Tennessee sandstone: (1) a constant injection rate, (2) a precyclic injection, and (3) a variable-rate injection test. All three tests were performed under the same principal stress conditions: vertical stress of 10.3 MPa (1500 psi), minimum horizontal stress of 3.5 MPa (500 psi), and maximum horizontal stress of 20.7 MPa (3000 psi). In total, 16 piezoelectric transducers were mounted around a cylindrical sample to record the AEs. We have performed postsignal processing to extract AE event attributes, including the amplitudes, signal-to-noise ratio, arrival time, event location (with the velocity-anisotropy input), and frequency analyses. The AE events associated with the constant-rate injection test possessed the lowest frequencies (150–270 kHz). The variable-rate test AE events possessed higher frequencies (160–310 kHz), whereas the precyclic injection had events with the highest frequencies, peaking at 330 kHz. Acoustic events before failure had lower amplitudes, but higher frequency compared to those recorded postbreakdown, suggesting different failure modes. Precyclic injection induced the greatest number of locatable events before and after failure.

Effect of geometry and thermal mass of Direct-Metal-Laser-Sintered aluminium Heat Exchangers filled with phase change materials on Lithium-Ion cells’ passive cooling

• Direct-Metal-Laser-Sintered (DMLS) aluminium Heat Exchangers (HEX) • DMLS HEX filled with Phase Change Materials (PCM) for Li-Ion cells isothermalisation. • Effect of PCM mass and HEX geometry on Li-Ion cells isothermalisation. • Single discharge and consecutive charge/discharge cycles tests conducted. This study investigates the effect of mass and geometry as design parameters of a Lithium-Ion (Li-Ion) cell Thermal Management System (TMS) based on a Direct-Metal-Laser-Sintered (DMLS) structure filled on Phase Change Material (PCM). As part of a TMS, complex heat exchanger geometries are produced using DMLS technique, filled with a PCM, and experimentally tested using an established methodology. The design parameters investigated are PCM mass and DMLS heat exchanger geometry to assess the effects of increased thermal energy storage capacity and enhanced equivalent thermal conductivity respectively on the overall performance of a Li-Ion pouch cell. Constant discharge rate tests and stress sequences are used to reproduce realistic Li-Ion cell operating conditions. It has been shown that all PCM TMS effectively improve the isothermalisation of the cell under a single discharge at rate 3C compared to natural convection and decreased the cell maximum temperature by at least 5 °C. The enhanced heat transfer performance of finned designs further improves the temperature uniformity and decreases the cell maximum temperature. When tested under stress sequences, the TMS characterised by a higher thermal mass maintained functional isothermalisation for 5 cycles; this is an increase of two cycles than for the TMS with a lower thermal mass. By using a Pareto front analysis based on thermal and geometrical variables, specific designs are indicated as the best combination of thermal performance and additional weight for single discharge tests (i.e., intermittent load) and stress sequences (i.e., constant load).

Усиление внутреннего слоя многослойного композита базальтопластиком в виде сотовой структуры

In our studies we present a multilayer structure consisting of outer layers of two-ply basalt composed of basalt fabric impregnated with an epoxy compound and an inner layer of polyurethane reinforced with basalt, having the same composition, formed in conjugate hexagonal prisms, and forming a cellular framework. The main part describes the technological sequence of obtaining basalt face layers, basalt hexagonal cellular frame, and filling it with a liquid reaction mass of rigid polyurethane system. The formation of a single multilayer composite structure is shown. We also present the results of the experimental research of strength of a laminated composite and its inner layer without facing layers when tested for static bending with concentrated load increasing at a constant rate and compression testing up to 10% of relative deformation. It describes the effect of the size of hexagonal prismatic cells of the frame on the physical and mechanical characteristics of the middle layer. The reduction of the cell size results in the increase of the composite strength. The dependence of the composite density on the size of the cells of the basalt frame has been studied.

Rib cage distortion and dynamic hyperinflation during two exercise intensities in people with COPD

BackgroundThe relationship between rib cage (RC) motion abnormalities, dynamic hyperinflation (DH), and exercise capacity in people with COPD is controversial. AimTo investigate RC distortion and operational chest wall volumes during moderate and high constant-rate exercises in people with COPD. MethodsSeven male participants [median(Q1-Q3) age: 63(60.0–66.0) years; FEV1: 39.0(38.0–63.0)% of predicted] performed a symptom-limited incremental exercise testing on cycle ergometer, followed by constant-rate tests (60 % and 80 % of peak work rate). Optoelectronic plethysmography was used to evaluate RC distortion: phase angle-PhAng, inspiratory phase ratio-PhRIB, expiratory phase ratio-PhREB; and chest wall volumes: end-inspiratory volume-Vei and end-expiratory volume-Vee. ResultsPhRIB and PhREB significantly increased during both constant-rate exercise tests, without difference between them. In general, Vei of the chest wall significantly increased in both exercise intensities while Vee did not change. ConclusionsThe occurrence of RC distortion seemed not to limit the exercise capacity in people with COPD evaluated, and it was present even in the absence of DH.

Strain softening of concentrated cohesive particulate suspensions prior to yield

We study the viscoelastic solid properties of cohesive particulate suspensions using creep and constant rate tests in a vane-in-large-cup geometry. A cup-to-vane diameter ratio larger than 4 is used to ensure that wall effects are minimized. In both the creep and constant rate tests, the modulus becomes nonlinear at strains consistent with scaled interparticle bond distances. Yielding and subsequent flow do not occur until strains of order 1, corresponding to a cage melting or particle crowding failure mechanism. In between the bond and cage melting strains, the modulus shows power-law softening with an index of approximately −0.8, corresponding to progressive bond breakage. The observed behavior in creep correlates with constant rate experiments and demonstrates that strain softening of the modulus prior to yielding is an important component of the rheology of particulate gels and suspensions. The assumption of linear behavior up to yielding appears to be inappropriate. We observe that the transient creep behavior initially shows power-law or Andrade creep that transforms to an exponential decay at long times. For creep stresses that show time-dependent yield, the break time decreases exponentially with stress.

Application of the Modified Incremental Step Test for Pulmonary Rehabilitation.

A Modified Incremental Step Test (MIST) performed in the home may facilitate entirely home-based pulmonary rehabilitation programs. The aims of this study were to investigate the reliability and responsiveness, and the utility of the MIST for exercise prescription in people with stable chronic lung disease. The MIST was undertaken at the center and home in random order, before and after pulmonary rehabilitation, with 2 tests at each time point. Reliability was assessed using intraclass correlation coefficient. Responsiveness was evaluated as effect size. The minimal important difference was appraised using distribution and anchor-based methods. In a substudy, physiological responses to MIST were measured by a portable metabolic system, followed by a constant step rate test at 60% of peak oxygen uptake (VO2peak), to evaluate utility for exercise prescription. Forty-six participants were recruited (29% of eligible candidates). There was excellent reliability for number of steps recorded in home- and center-based settings (intraclass correlation coefficient = 0.954, 95% CI = 0.915-0.976). A small-moderate effect size was demonstrated following pulmonary rehabilitation (0.34), and the minimal detectable change was 7 steps. All participants in the substudy achieved 60% of VO2peak and achieved steady state by the fourth minute, with 60% of VO2peak corresponding to a mean 37% (95% CI = 29-44) of the MIST final level. The MIST is reliable and responsive to pulmonary rehabilitation in people with stable chronic respiratory disease. It provides new opportunities to assess exercise capacity, prescribe exercise training, and reassess exercise program outcomes in environments where established field walking tests are not feasible. Pulmonary rehabilitation is a highly effective treatment that is underutilized worldwide. Home-based pulmonary rehabilitation may improve access for patients and deliver equivalent clinical outcomes but is limited by the availability of a robust exercise test that can be used at home to assess exercise capacity and prescribe training intensity. This study tested the clinimetric properties of the MIST and demonstrated a new way to assess exercise capacity, prescribe exercise training of an appropriate intensity, and reassess exercise capacity in environments where established field walking tests are not feasible.

Effects of Superimposed Pressure on the Mechanical Properties of HTPB Propellant in a Wide Temperature Range

AbstractConsidering the propellant of solid rocket motor with tube grain is in the state of superimposed pressure after ignition, the effect of pressures, temperatures, and tensile rates on the mechanical properties of solid propellant were investigated together. A test system with wide temperature‐ambient pressure range was developed to investigate the effects of superimposed pressure on the performance of propellant. The uniaxial constant tensile rate tests for a certain HTPB propellants under different superimposed pressures and temperatures were performed at different tensile rates. Research shows that there are no apparent dewetting points in the propellant stress‐strain curves under superimposed pressures. Moreover, the performance of propellant under superimposed pressure related to propellant itself such as composition of the propellant was evaluated by comparing to another propellant. Relevant methods and conclusions can provide a reference for structural analysis and storage life prediction of solid rocket motors.

The effect of piezoceramic volume fraction on properties of three-phase piezocomposites

In this study, three-phase piezocomposites are fabricated on the basis of the 1–3 composite structure and the cutting–filling method. The 1–3 piezocomposites are used with PZT-5A as the piezoelectrics and epoxy/silicone rubber as the matrix. The relationships between the performance parameters of the 1–3 composites and different ceramic volume fractions are analyzed via finite element simulation and experimental measurement. Composite samples with volume fraction of 0.20.8 are prepared through an experiment and tested using an impedance analyzer and a piezoelectric constant tester. Simulation results agree well with experiment results, thereby indicating that the composites have a high electromechanical coupling coefficient.

Brittle‐Ductile Deformation and Tensile Rupture of Dome Lava During Inflation at Santiaguito, Guatemala

AbstractGas‐and‐ash explosions at the Santiaguito dome complex, Guatemala, commonly occur through arcuate fractures, following a 5‐ to 6‐min period of inflation observed in long‐period seismic signals. Observation of active faults across the dome suggests a strong shear component, but as fault propagation generally proceeds through the coalescence of tensile fractures, we surmise that explosive eruptions require tensile rupture. Here, we assess the effects of temperature and strain rate on fracture propagation and the tensile strength of Santiaguito dome lavas. Indirect tensile tests were conducted on samples with a porosity range of 3–30% and over diametral displacement rates of 0.04, 0.004, and 0.0004 mm/s. At room temperature, the tensile strength of dome rock is rate independent (within the range tested) and inversely proportional to the porosity of the material. At eruptive temperatures we observe an increasingly ductile response at either higher temperature or lower displacement rate, where ductile deformation is manifest by a reduction in loading rate during constant deformation rate tests, resulting in slow tearing, viscous flow, and pervasive damage. We propose a method to conduct indirect tensile tests under volcanic conditions using a modification of the Brazilian disc testing protocol and use brittleness indices to classify deformation modes across the brittle‐ductile transition. We show that a degree of ductile damage is inevitable in the lava core during explosions at the Santiaguito dome complex and discuss how strain leading to rupture controls fracture geometry, which would impact gas pressure release or buildup and regulate explosive activity.

Equivalent Principle of Time‐Temperature‐Strain Rate for Poisson's Ratio of Composite Solid Propellant

AbstractThe viscoelastic Poisson's ratio of solid propellant seriously affects the analytical accuracy of the structural integrity of the solid rocket motor. Based on the digital image correlation (DIC) method, a stress relaxation test and a uniaxial constant tensile rate test were carried out to measure the viscoelastic Poisson's ratio of the composite solid propellant according to the stress characteristics of solidification cooling and ignition pressurization conditions. The effects of time, temperature, longitudinal strain as well as tensile rate on the viscoelastic Poisson's ratio of propellant were studied. In this paper, the main curves of the temperature and strain rate of the propellant Poisson's ratio at the reference temperature of 25 °C and the main curves of temperature and longitudinal strain at the reference time of 10000 s were established. The research shows that the viscoelastic Poisson's ratio of composite solid propellants increased with increasing temperature, longitudinal strain and tensile rate. Under the solidification cooling condition, the Poisson's ratio of the solid propellant does not change significantly with time. At this point, the Poisson's ratio can be regarded as a constant, but the appropriate value must be selected according to the operating temperature and initial deformation of the solid rocket motor. In the uniaxial constant tensile rate test, when the stretching rate reached 500 mm/min, Poisson's ratio of the propellant gradually approached a certain constant value. Considering that the loading rate of the propellant is generally above 0.5 s−1 under the ignition pressurization condition, the strain rate is large, the Poisson's ratio of the propellant can be taken as a constant. Relevant methods and conclusions can provide a reference for structural analysis and storage life prediction of solid rocket motors.

A Forchheimer's law-based analytical model for constant-rate tests with linear flow pattern

Aquifers with quasi-linear flow pattern are frequently envisaged in fractured zones, in oil, gas or enhanced geothermal reservoirs, or in civil engineering where cut-off walls are constructed. The water flow towards a well in this linear aquifer system has been long investigated under Darcian flow condition, but remains an open issue for non-Darcian flow. In this study, a general linearization approximation strategy is suggested for the Forchheimer equation, and an analytical solution is proposed by using Laplace transform for non-Darcian flow towards a well in aquifers laterally bounded by no-flow barriers. Numerical simulations using the finite volume method prove that the linearization approximation performs best when it takes the mean of two commonly-used strategies, and the analytical model is sufficiently accurate at late times for observation wells located moderately far from the source. The proposed model was applied to data interpretation of the pumping tests at the Changheba dam foundation bounded by two cut-off walls in Southwest China, where the drawdown curves can be divided into 1D flow, transitional flow and 2D flow stages as a result of lateral flow through weathered bedrocks at late times. The proposed model provides a valuable tool for characterizing the hydraulic properties of aquifers and reservoirs with a linear flow pattern and for assessing the possible leakage through the lateral barriers by type curve matching.

Development of Probabilistic Viscoelastic Continuum Damage Model for Asphalt Concrete

The main objective of this paper is to develop a realistic probabilistic framework for characterization of different types of asphalt concrete using advanced material modeling. The adopted methodology builds on and enhances a viscoelastic continuum damage (VECD) material model by utilizing a suite of associated experimental testing protocols and incorporating the uncertainties associated with the different material properties. The modeled uncertainties address the variabilities and errors associated with the linear viscoelastic (LVE) functions achieved from the complex modulus test and damage characteristic curves obtained from constant crosshead rate testing. A probabilistic scheme using First Order approximations and Monte Carlo simulations is developed to characterize the inherent uncertainty of each of the LVE functions over the time domain of their mastercurves. For damage characteristic curves, the uncertainty in normalized pseudostiffness increases as the level of damage becomes larger. The uncertainties of LVE properties are propagated along with those of C versus stress curves to yield a probabilistic viscoelastic continuum damage model (P-VECD). The P-VECD not only predicts the average viscoelastic response to a given loading input, but it can also provide its distribution, which is essential for a reliability-based pavement design.

Combined role of leaky and non-Darcian effects on the flow to a pumping well with a non-uniform flux well-face boundary

In this study, a non-Darcian flow model was developed for a constant-rate test of a partially penetrating well with a non-uniform flux boundary in a leaky confined aquifer. The Izbash equation was applied to describe non-Darcian flow in the radial direction. Both analytical and numerical methods were employed to solve this model. It was found that the analytical solution with linearization was adequate only when non-Darcian effects were relatively small. With the finite difference method, the radial and vertical fluxes along the well screen were analyzed under four different cases involving leaky and non-Darcian effects. The leaky and non-Darcian effects on the drawdowns with non-uniform flux (NUF) boundary were compared with those with uniform flux (UF) boundary. The results indicate that both leaky and non-Darcian effects can reduce the fluxes along the well screen, while non-Darcian effects can diminish the leakage-induced differences of flux and drawdown between the two well screen ends. Non-Darcian effects can reduce the differences between UF and NUF drawdowns at any elevation with the greatest reduction difference at the elevation of the top end of the screen. The UF solution can replace the NUF solution when the distance is far from the well, as this distance is smallest at the elevation of the screen midpoint and can be distinctly reduced by non-Darcian effects. In general, the results are most sensitive to the power index n, moderately sensitive to the other aquifer parameters and least sensitive to the parameters of the aquitard.

Hydrogeological characterization and parameters estimation of the aquifer close to the Adige River (Verona, Italy) for the design of deep excavations

In the framework of the final design of a new hydroelectric plant close to the existing dam on the Adige River in the municipality of San Giovanni Lupatoto (VR, Italy), the design of deep excavations in loose sediments below groundwater level, and the connected risks of piping and excavation bottom heave required a detailed study of hydrogeological characterization, aimed to an accurate aquifer parameterization and so a confident design of excavation supports and dewatering systems. Particularly a three-dimensional analysis of the problem was necessary, because the hydrogeological system was complicated by many “artificial” boundary conditions (dam on the river, deep foundations of the existing and new engineering works) causing vertical not negligible flow paths. The conceptual model has been developed applying, in parallel, different prospecting tools: a preliminary Step Drawdown Test, a long duration Constant Rate Test, a multiple tracing test and the implementation of a three-dimensional numerical model of groundwater flow (MODFLOW-2005 code) and advective transport (MODPATH code). The modeling has allowed a good estimate of the aquifer parameters such as hydraulic conductivity and effective porosity through calibration of the pumping/tracing tests under transient conditions. Moreover, the simulation of post operam conditions and the comparison with ante operam, in terms of flow paths length and filtration velocity, showed that the construction of the new works foundations would have determined a sensitive reduction of groundwater velocities closed to the existing dam.

Laboratory Performance Evaluation of HMA Modified with Various Types and Contents of Polymer

Since asphalt binder modifiers for the performance improvement have both good and bad effects on the performance of asphalt pavements, it is important to consider all performance parameters of asphalt pavements for the development of modifiers. This paper evaluates the viscoelastic and plastic properties of four types of asphalt mixtures (three modified mixtures and one unmodified mixture) by laboratory tests, and then, the test results are employed to investigate the effects of modifiers. Test methods adopted in this study are the dynamic modulus test for linear viscoelastic model classified as nondefective test and tension test for constant crosshead rate test and cyclic load test and the triaxial compression test for plastic deformation classified as defective test. The performance for the fatigue failure at the real site’s pavement was evaluated by using the VECD-FEP++. The performance of rutting for each mixture was evaluated by using the viscoplastic model from tension test and triaxial compression test proposed by NCHRP 1-37 A MEPDG (AASHTO2004) and the rutting model. The findings from this study support general understanding of the effects of asphalt binder modifier on the fatigue cracking and rutting performance. When considering the performances of rutting and fatigue failure, K2 mixture is the best SBS-modified material. The modified agent for K1 mixture has low performance than K2 mixture, and K4 mixture is good when the rutting is terribly occurred. But it needs serious caution to the failure.

Field Permeability Tests: Importance of Calibration and Synchronous Monitoring for Barometric Pressure Sensors

Pressure transducers (PTs) and an atmospheric pressure transducer (APT) were used to register test data during two types of permeability tests, which were performed in 14 wells monitoring a confined aquifer installed in the lab, and a field rising-head test in clay. The constant-head tests were performed using a peristaltic pump and thus functioned as constant flow rate tests until stabilization of the water level in the well riser pipe. The rising-head tests were started by the sudden removal of a slug of water. This article presents, first, the method used to calibrate the transducers to assess their systematic calibration error (offset) values. Then, it quantifies the influence of synchronized monitoring for the (PT-APT) pair on short- and long-term test data, which had never been done before. The results indicate that the pair calibration cannot be neglected and that the synchronized monitoring is important for all tests, except maybe for a short-duration variable-head test. For most tests, however, the barometric fluctuation with time plays a significant role.

Fatigue properties of crumb rubber asphalt mixtures used in railways

The use of asphalt mixtures in railway tracks provides a positive contribution to the bearing capacity, stability, durability and more importantly damping properties of the railway structure particularly for the new generation of low-vibration-railway track systems. However, one of the main concerns in the use of asphalt mixtures in railways is their fatigue cracking caused by the repeated traffic loading. The present study focused on the fatigue damage behavior of asphalt mixtures in the railways through using the viscoelastic continuum damage theory. Three experiments of creep compliance, constant crosshead rate and cyclic fatigue tests were carried out on some asphalt mixtures with different air void contents and aging conditions. Based on the results obtained, the crumb rubber modification of railways asphalt mixtures at low stress levels increases the fatigue life of asphalt up to 7.2 times while this increase is at the most 3.6 for the highway asphalt mixture. Furthermore, reducing the air void content from 4% to 2% for the crumb rubber modified asphalt mixture increases the fatigue life by 9.4 times at high stress levels and 18.2 times at low stress levels, which is a great improvement. It was shown that the lowest fatigue life is obtained in the aged crumb rubber modified mixture (i.e., 20 percent of unmodified asphalt mixture).