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The application of recycled aggregate is crucial for waste concrete recycling, while the loading rate significantly influences the fracture behavior of recycled aggregate concrete. Herein, we investigate the effect of loading rate on the flexural and fracture behaviors of recycled aggregate concrete, along with associated acoustic emission characteristics. Results show that the flexural strength and energy absorption capacity maximum increase by 15.18% and 38.39%, respectively, as the loading rate rises. As the loading rate increases from 0.05 to 1 mm/min, peak frequency is primarily clustered in 0 ~ 75 kHz and 75 ~ 225 kHz and tends to be dense, while the b value decreases by 19.28%, 23.30%, and 30.17%, respectively. Additionally, the proportion of shear failure also decreases, which relates to the high energy release rate. Further, the multifractal spectrum α − f(α) resembles a quadratic distribution, with both multifractal intensity ∆f and spectrum width ∆α showing a downward trend as the loading rate rises. [ABSTRACT FROM AUTHOR]

Ice compressive strength is a key property for investigating the interaction between ice and structures. In this research, a digital image correlation (DIC) technique is developed to measure the complete deformation range of ice samples in uniaxial compression tests that were conducted at different temperatures and loading rates. This method overcomes the limitations of traditional deformation measurement techniques, such as low accuracy and single-point measurements. The ice specimens are generated with initial fibrous pores instead of sphere pores for simulation. This innovative method enables the shear and splitting failure modes to be captured, which are consistent with the test results in this research. The experiments and numerical simulations reveal that the compressive strength increases when the temperature decreases and the loading rate increases. In contrast, the maximum strain decreases with lower temperatures and higher loading rates. This research introduces a novel numerical simulation procedure to study compressive ice deformation and offers experimental approaches for real-time and noncontact measurement of ice deformation at low loading rates. Practical Applications: In this research, several experiments are conducted at three different temperatures (−25°C, −30°C, and −35°C) and loading rates (1, 3, and 5 mm/min). The experimental observations reveal that varying failure modes depend on the strain rate. In addition, a correlation between the compressive strength, temperature, and strain rate is confirmed. In addition, this research investigates the application of digital image technology (DIC) for the real-time and noncontact measurement of ice deformation. The use of noncontact strain measurement technology overcomes the limitations of traditional deformation measurement methods. In addition, noncontact measurements could improve the precision and dependability of ice deformation monitoring and provide more accurate observations and a better understanding of ice behavior. In addition, it could be used in future applications in this field, which opens up new research possibilities concerning ice deformation. This new technique offers a valuable contribution to advancing ice deformation measurement research. [ABSTRACT FROM AUTHOR]

Copyright of Urban Geology is the property of Urban Geology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To investigate the influence of loading rate on the local deformation and failure characteristics of rock-like models with a locked segment, this study fabricated them using quartz sand and barite powder as aggregates, and gypsum as cementing material. Uniaxial compression tests, combined with strain cube monitoring and the digital image correlation technique, were employed to analyze the mechanical properties, internal and external deformation characteristics, crack propagation, and failure modes at different loading rates. The results showed that as the loading rate increased, the strength of these models initially increased significantly and then slightly decreased, primarily due to the complex interaction between the longitudinal and transverse deformations of the models and the stress concentration intensity at the crack tips. The fluctuation in the principal strain axis's deflection angle revealed the complex process of stress wave propagation and particle adjustment within the models, with more pronounced fluctuations observed at higher loading rates. The stress intensity factors, KI and KII, at the crack tips first increased and then decreased with increasing loading rate, with KI consistently higher than KII. The strain concentration phenomenon in the rock-like models occurred earlier with increasing loading rates, and the corresponding crack closure stress exhibited a decreasing trend. Higher loading rates caused earlier crack initiation and faster propagation. As the loading rate increased, the crack paths shortened, and both damage density and severity increased significantly, indicating brittle failure. This study provides important experimental evidence and theoretical support for understanding the effects of loading rate in rock mass engineering.

Abstract In order to study the mechanics, acoustic emission (AE) and electromagnetic emission (EME) response law of bursting liability coal at different loading rates, uniaxial compression tests were carried out on coal mass from Konggu Coal Mine. The corresponding relations among mechanical properties, AE and EME signals in the process of coal failure under loading were analyzed, and the energy evolution law of coal failure with bursting liability under loading rate was discussed. The results show that within a certain range of loading rate, the higher the loading rate, the higher the compressive strength and peak load of bursting liability coal, and the shorter the time for coal to reach the peak load. Under different loading rates, the mechanics, AE and EME signals of coal samples can be well corresponded. When the loading rate is low, the number of blocks destroyed of coal sample is large and the block size is relatively small, and the blocks are mainly scattered around the test platform. When the loading rate is high, the number of damaged blocks is relatively small and the block size is relatively large, and the blocks are far away from the test bench. When loading at a low rate, the internal cracks in coal can be fully developed and connected, and the energy release rate is relatively uniform in the process of loading and failure of coal sample. In the case of high loading rate, the energy release rate of coal sample in the loading process is much smaller than that in the moment of failure. Combining the above test results with the actual situation of the working face, it can be concluded that the total energy stored in the coal of fast mining increases and the threshold of impact decreases compared with that of slow mining. Therefore, under the disturbance of external dynamic load, rapid mining is more likely to induce rock burst.

The digital image correlation (DIC) technology was used to investigate the evolution law of the coal surface strain field under different loading rates and to analyze the influence of loading rate on the evolution of the deformation field, deformation localization, and surface deformation energy density. The experimental results indicate that the higher the loading rate is, the more complete the final failure mode of the coal body, and the failure mode of the coal body also transitions from shear failure to tensile failure; the loading rates of different magnitudes also affect the localization time of coal deformation. The higher the loading rate is, the greater the proportion of the initiation time of coal deformation localization to the overall failure time. The higher the loading rate is, the more obvious the growth trend of deformation energy density before deformation localization, and the more energy accumulates in the surface deformation localization area; the qreater the stress at the start time of deformation localization.

To clarify the mechanical characteristics of tight sandstone in the Cretaceous Bashijiqike Formation of Kuqa Depression in Tarim Basin, and address field issues in deep and ultra-deep oil and gas exploration and development, triaxial compression experiments were used to quantitatively study the patterns of changes in rock mechanical properties influenced by confining pressure, fluid, and loading rate, with a preliminary analysis of their causes. The results showed that the maximum principal stress difference and elastic modulus of the sandstone samples increased significantly with confining pressure. The micro-reason was that the increase in confining pressure reduced the distance between particles inside the rock, enhancing the rock's cohesion and making particle dispersion less likely. Sandstone samples exhibited a progression from brittleness under low confining pressure to brittle-ductile transformation, and to ductile deformation under high confining pressure. Compared with dry sandstone samples, the reduction in the elastic modulus of samples soaked in pure water, 150 g/L solution, 250 g/L solution, and 350 g/L solution were 67.71%, 61.45%, 64.69%, and 57.32%, respectively, with pure water soaking causing the greatest reduction. Increasing fluid salinity could mitigate the weakening trend in rock mechanical parameters. Crystallization on crystal surfaces and changes in the electric double layer thickness were important controlling factors for these patterns. At lower loading rates, the values for maximum principal stress difference, elastic modulus, and Poisson's ratio of the sandstone samples were smaller, but they increased faster with increasing loading rates. When the loading rate reached a certain critical value (around 0.05 mm/min in this experiment), the rate of increase in rock mechanical parameters slowed down.

Based on the laboratory uniaxial compression test, a numerical model was established by particle flow software and the microscopic parameters were calibrated. The stress-strain curves, the number of micro-cracks, the failure process and the change of microscopic displacement field of gangue cemented backfill samples were studied under different loading rates. The results show that the peak strength and elastic modulus of the sample increase with the increase of loading rate. The number of microcracks is proportional to the loading rate; the microcrack-strain curves can be divided into three stages: no crack initiation, rapid crack growth and stable crack number; the failure process of the sample is divided into four stages: compaction, elastic deformation, plastic failure and residual deformation; the particles on both sides of the microcrack of the sample have different forms of combined failure, including tensile failure, shear failure and mixed failure of tensile and shear action.

In order to study the influence law of energy evolution characteristics of coal confined passively by CFRP sheets. A series of uniaxial compression tests of coal confined passively by CFRP sheets were carried out under different loading rates by the SAM–2000 rock mechanics test systems. The research results show that with the increase axial deformation, the total energy of coal confined passively by CFRP sheets first increase gradually with a “fovea inferior”, and then reaching a stable slope. The stable slope in the single-sheet condition is smaller than that in the double-sheet one, and the increase of the slope is larger than that of the latter one, but the stable slope at the maximum loading rate is cliff-like steep increase. With the increase of CFRP layers, the total energy of coal at peak and its growth ratio also increases. The effect of CFRP layers on the total energy of coal at peak and its growth rate is significantly better than that of the loading rate. The function evolution law of the total energy growth rate at peak under different rates is obtained and established a response surface considering rate and CFRP layers. When the loading rate is at its minimum or maximum, the dissipated energy rate growth ratio at peak decreases with the increase of CFRP layers, and the value at the maximum loading rate is about 6.03−8.87 times more than the value at the minimum rate. In the loading rate ranges from 1.67×10−3 mm/s to 1.67×10−2 mm/s, the peak dissipation energy rate and its growth ratio also increase with the increase of the CFRP layers. The function evolution law of the dissipated energy rate growth ratio at peak under different loading rates is obtained, and the response surface considering both loading rate and CFRP layers is also established. With the increase of axial deformation, the elastic energy consumption ratio of CFRP passively confined coal has a transition from rapid steep drop to steady inflection point and then from slow increase to rapid steep increase, which is like a “fishhook” shape. The elastic energy consumption ratio near the peak shows a continuous step mutation, indicating that cracks are developing rapidly.

Understanding the effects of microwave irradiation and thermal treatment on the dynamic compression and fragmentation properties of rocks is essential to quantify energy consumption in rock engineering. In this study, Fangshan granite (FG) specimens were exposed to microwave irradiation and heat treatment. The damage of FG specimens induced by these two methods was compared using X-ray CT scanning and ultrasonic wave method. The temperatures of FG after microwave irradiation and thermal treatment were effectively evaluated using a newly proposed technique. A novelty method for precisely determining the geometric features of fragments is developed to estimate the fragmentation energy. Thus, the dynamic uniaxial compressive strength (UCS), the dynamic fragmentation characteristics, and the fragmentation energy of FG after these two pretreatment methods can be reasonably compared. The noticeable distinction of loading rate effect on the dynamic UCS of FG between these two pretreatment methods is first observed. A relationship is established between the dynamic UCS and the damage induced by microwave irradiation and heat treatment. Moreover, fragmentation energy fan analysis is introduced to accurately compare the fragmentation properties of FG after two pretreatment methods in dynamic compression tests.

In order to study the mechanics, acoustic emission (AE) and electromagnetic emission (EME) response law of bursting liability coal at different loading rates, uniaxial compression tests were carried out on coal mass from Konggu Coal Mine. The corresponding relations among mechanical properties, AE and EME signals in the process of coal failure under loading were analyzed, and the energy evolution law of coal failure with bursting liability under loading rate was discussed. The results show that within a certain range of loading rate, the higher the loading rate, the higher the compressive strength and peak load of bursting liability coal, and the shorter the time for coal to reach the peak load. Under different loading rates, the mechanics, AE and EME signals of coal samples can be well corresponded. When the loading rate is low, the number of blocks destroyed of coal sample is large and the block size is relatively small, and the blocks are mainly scattered around the test platform. When the loading rate is high, the number of damaged blocks is relatively small and the block size is relatively large, and the blocks are far away from the test bench. When loading at a low rate, the internal cracks in coal can be fully developed and connected, and the energy release rate is relatively uniform in the process of loading and failure of coal sample. In the case of high loading rate, the energy release rate of coal sample in the loading process is much smaller than that in the moment of failure. Combining the above test results with the actual situation of the working face, it can be concluded that the total energy stored in the coal of fast mining increases and the threshold of impact decreases compared with that of slow mining. Therefore, under the disturbance of external dynamic load, rapid mining is more likely to induce rock burst. [ABSTRACT FROM AUTHOR]

Adhesive bonding has become increasingly popular in the aeronautic and automobile sectors due to its ability to reduce weight, create strong bonds, and join dissimilar materials. The primary aim of the study is to conduct experimental analysis on Single-Lap Joints (SLJs), specifically focusing on varying ambient temperatures from (25°C to 65°C) while keeping the loading rate constant at 1.3 mm/min. This study used SAE 1020 steel, AA2024-T3, and BK-9 adhesive to manufacture SLJs. The adhesive-bonded SLJs were developed using dissimilar and similar adherends. The thermal behavior of the BK-9 adhesive was examined by conducting Digital Scanning Calorimetry (DSC) and Thermal Gravimetry Analysis (TGA) before and after subjecting it to elevated temperatures. The bonding quality has been examined using ultrasonic testing. The failure strength of the adhesive bond on SLJs was performed at the Universal Testing Machine (UTM) using tensile testing equipment, and a Field Emission Scanning Electron Microscope (FESEM) was utilized to determine the failure patterns. The result indicate that the SAE 1020-SAE 1020 steel joints exhibited superior mechanical behaviour, showing the highest failure load of 5.120 kN at 25°C room temperature, respectively. [ABSTRACT FROM AUTHOR]

A novel electro-hydraulic servo point load meter has been developed to address the limitations of existing point load meters, which cannot provide continuous and uniform loading. This new meter enables continuous and uniform loading with variable rates, thereby reducing the dispersion of test data and offering a technical solution for revising the current point load strength calculation formula. Experimental investigations were conducted to analyze the influence of loading rates (0.1 kN/s, 0.5 kN/s, 1.0 kN/s) on the existing point load strength correction method. Four types of rock samples, namely, fine-crystalline granite, coarse-crystalline granite, siltstone and marble, were utilized in the study. Each rock sample was tested at four different sizes: 203 mm3, 303 mm3, 403 mm3, 503 mm3. The objective was to examine how the loading rate affects the accuracy and effectiveness of the point load strength correction method. Initially, the correction index "m" from various domestic and foreign regulations was employed to calculate and analyze the test data, determining the appropriate correction index m, loading rate, and range of rock sample sizes. Subsequently, the relationship between the standard point load strength and uniaxial compressive strength was analyzed based on these findings. The research results indicate the following: (1) the larger the strength of the rock sample, the smaller the point load correction index m and all four rock samples demonstrated an increase in standard point load strength when solved using the four correction indices (m1, m2, m3, m4) with increasing loading rate. (2) With increasing sample size, the standard point load strength solved using correction indices m2, m3, m4 still exhibited a significant size effect, while the dimensional effect of the standard point load strength solved using m1 was not evident. (3) The conversion factors obtained through zero-intercept linear regression analysis for fine-crystalline granite, coarse-crystalline granite, siltstone, and marble were 16.45, 15.38, 15.17 and 14.83, respectively. These results indicate that the conversion factors for rocks with lower strength are smaller compared to those with higher strength. Highlights: The impact of four different rock samples with varying sizes on the existing point load strength correction method is analyzed under three loading rates. An investigation is conducted to determine the appropriate point load strength correction index for the four rock samples. The study identifies the optimal loading rate and size range for rock samples based on the modified correction index. The relationship between standard point load strength and uniaxial compressive strength is examined. [ABSTRACT FROM AUTHOR]

Assessing the dynamic properties of rocks remains a foundational pursuit in the field of rock engineering, providing crucial insights into their mechanical behaviors across a spectrum of loading conditions, including static, cyclic, and dynamic scenarios. This paper expounds upon the utilization of the nonresonance (NR) torsional shear test and its implications for understanding rock responses, particularly in the context of low and medium loading rates. The NR method serves as a pivotal tool for investigating model rock materials subjected to loading conditions characterized by low frequencies and amplitudes. Renowned for its efficacy, this method allows the simultaneous determination of two critical dynamic parameters: shear modulus (G) and damping ratio (D), all at a specific loading frequency. It has been ascertained that the loading rate increased as the loading frequency and applied amplitude of loading increased. With increasing loading rate, the shear modulus consequently increased while the damping ratio decreased. It is observed that the dynamic responses of both ramp and sinusoidal loading waveforms increase concurrently with the amplitudes of the applied torque and loading frequencies. The sinusoidal waveform exhibits greater dynamicity than the ramp waveform at a certain loading rate. Furthermore, this study delves into the intricate analysis of the nonlinear viscoelastic dynamic response exhibited by rocks, utilizing the modified hyperbolic (MH) model and the Ramberg–Osgood (RO) model as analytical tools. The findings derived from curve fitting exercises unequivocally underscore the superior applicability of the Ramberg–Osgood model, particularly in characterizing modulus reduction behavior. Conversely, the modified hyperbolic model emerges as the preferred choice for comprehensive damping ratio analyses. This study enhances the comprehension of rock dynamics and responses under diverse loading conditions, contributing valuable understanding to rock engineering. Insights into loading and strain rate effects aid informed decisions and preventive measures for rock deformation and collapse risks. Practical Applications: This research suggests vital findings regarding the response of intact model materials to various dynamic loading conditions, providing significant insights for comprehending the mechanical response of rock structures exposed to cyclic loading conditions, which have the potential to create weaknesses in rocks resulting in untimely failures. The research can be utilized to assess the response of rocks in the context of seismic incidents, specifically those characterized by shear waves at particular frequencies. This study evaluates the response of rocks during earthquakes by establishing a correlation between the amplitude of torsional shear loading and the peak ground displacement linked to seismic events. In addition to its seismic implications, this research aids in advancing accurate predictive models and instruments that assess the stability and integrity of rock formations under different loading rates—a consequence of the symbiosis between frequency and amplitude. Professionals may ensure efficient risk mitigation, make well-informed decisions, and execute preventative measures concerning rock collapse and deformation by virtue of their comprehensive awareness of the delicate relationship between loading rate and dynamic rock properties. Incorporating the findings into engineering design standards and codes can bring about substantial improvements, augmenting the overall reliability and protection of rock structures. [ABSTRACT FROM AUTHOR]

Flatfoot is a structural and functional deformity of the foot that might change ground reaction force variables of gait. Evaluating the components of ground reaction force in three dimensions during gait is considered clinically important. This study aimed to investigate the components of ground reaction force, impulse, and loading rate during gait in people with flexible and rigid flatfoot compared to healthy subjects. 20 young women with flatfoot in two experimental groups (10 with rigid flatfoot and 10 with flexible flatfoot) and 10 healthy women in the control group participated in this study. Ground reaction force components during gait were measured using two force plates. The peak of ground reaction forces, impulse, and loading rate were then extracted. Data were processed and analyzed using MATLAB and SPSS software. One-way ANOVA with a significant level (P˂0.05) was used for statistical analysis. The results showed that peak braking force was higher in the rigid flatfoot group than in the control group (p = 0.016) and the flexible flatfoot group (p = 0.003). The posterior force loading rate was significantly higher in the rigid flatfoot group than in the flexible flatfoot group (P = 0.04). There was no significant difference in vertical loading rate between groups (P˃0.05). Since the maximal posterior ground reaction force was higher in the subjects with rigid flatfoot than in those with flexible flatfoot and healthy subjects, the increase in posterior ground reaction force is associated with an increase in anterior shear force at the knee. [ABSTRACT FROM AUTHOR]

Copyright of Petroleum Geology & Experiment is the property of Petroleum Geology & Experiment Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper introduces a new method for developing Autoclaved Aerated Concrete (AAC) blocks, investigating the impact of different loading rates on compressive strength and failure behaviour. Alkaline solution and accelerated curing tank curing were explored as alternatives to conventional methods using aluminium powder and autoclave curing with fly ash. Construction and demolition waste was used as a substitute for fly ash, and chopped steel wool fibres were added to enhance block strength. The blocks were tested under various loading rates, and stress–strain graphs were generated to calculate Young's modulus of elasticity values. ANSYS software was used for simulation and comparison, validating the accuracy of analytical models. The study shows a correlation between experimental and simulated values, confirming the successful incorporation of CDW and CSWF in AAC block development. Increasing the loading rate during testing leads to lower measured Young's modulus, indicating strain rate dependency. However, including CSWF enhances Young's modulus by redistributing stress and restraining crack propagation. The research contributes to understanding AAC's mechanical properties and performance, supporting its potential as a sustainable alternative for masonry materials in structural applications. [ABSTRACT FROM AUTHOR]

Fracture energy from semicircular bending tests is commonly used to measure the fracture resistance of asphalt mixtures. A study was conducted to develop master curves for the macrocracking of asphalt mixtures. The study examined four testing temperatures, five loading rates, two binder types, and two nominal maximum aggregate sizes (NMASs). Fracture energy was captured at different loading rates and temperatures, and a preliminary master curve was built using the dynamic modulus master curve approach. However, the initial plot of fracture energy versus reduced loading rate did not show a consistent trend. Instead, a parabolic shape was found in the local fracture energy when increasing the loading rate, and peak values were plotted for each temperature to produce the master curve for the macrocracking of asphalt mixtures. The maximum fracture energy was unique for each combination of NMAS and asphalt binder type and occurred at a specific temperature, indicating a new methodology for classifying the cracking resistance of asphalt mixtures: macrocracking master curves. Maximum values fell between typical low-temperature and intermediate-temperature fracture testing, highlighting a gap in understanding regarding macrocracking behavior. [ABSTRACT FROM AUTHOR]

A three‐dimensional non‐isothermal phase field model of polycrystalline NiTi shape memory alloy (SMA) was established based on the Ginzburg–Landau's theory, which considered the interaction between crack growth and martensite transformation (MT). Then, the crack propagation of polycrystalline NiTi SMA and its dependence on the system's grain size and loading rate were studied by the phase field simulations. The results show that the proposed phase field model can characterize the MT behavior, temperature field changes, and stress‐displacement response of NiTi SMA during the crack growth with different grain sizes and loading rates. That is the higher the loading rate, the higher the fracture toughness is; the larger the grain size, the higher the fracture toughness is and the more significant the influence of grain boundary on the crack growth path becomes. Meanwhile, as the grain size increases, the fracture mode gradually changes from the transgranular fracture (for the fine‐grained alloy with a grain size ≈ 15 nm) to the intergranular one (for the coarse‐grained alloy with a grain size ≈ 100 nm). Highlights: The mechanisms for the rate dependence of crack propagation are clarified.The influence of the latent heat effect on crack propagation are clarified.The mechanisms for the toughening effects under different grain sizes are clarified.The mechanisms for the change in fracture mode are clarified. [ABSTRACT FROM AUTHOR]

In this paper, the shear modulus and damping ratio of silica rock under cyclic loading were experimentally analyzed using two loading modes, constant amplitude and increasing amplitude, combined with three increasing loading rates. Observations have indicated a decrease in the shear modulus of specimens as the number of cycles increased during the loading and unloading phases and an overall increase with larger amplitude intervals. The change in loading rate significantly affects the damping ratio of the specimens, leading to a stepwise decrease within the same cyclic group, while the damping ratio of a single specimen exhibits a 'concave' distribution throughout the cyclic interval. Based on the axial strain and dissipation energy, this paper develops two damage models that can effectively predict the damage accumulation process in rocks under cyclic loading. These findings have significant implications for a deeper understanding of the mechanical behavior of rocks under dynamic loading and offer theoretical guidance and technical support for rock engineering. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of High Pressure Physics is the property of Chinese Journal of High Pressure Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In nature, rock masses often exhibit fissures, and varying external forces lead to different rates of loading on fissured rock masses. By studying the influence of the loading rate on the mechanical properties of fractured rock mass and AE characteristic parameters, it can provide a theoretical basis for the safety and stability prediction of engineering rock mass. To investigate the influence of loading rates on fissured rock masses, this study utilizes surrogate rock specimens resembling actual rock bodies and prefabricates two fissures. By conducting uniaxial compression acoustic emission tests at different loading rates, the study explores changes in their mechanical properties and acoustic emission characteristic parameters. Research findings indicate the following: (1) Prefabricated fissures adversely affect the stability of specimens, resulting in lower strength compared to intact specimens. Under the same fissure inclination angle, peak strength, elastic modulus, and loading rate exhibit a positive correlation. When the fissure inclination angle varies from 0° to 60° under the same loading rate, the peak strength of specimens generally follows a "V"-shaped trend, decreasing initially and then increasing, with the minimum peak strength observed at α = 30°. (2) Prefabricated fissure specimens primarily develop tensile cracks during loading, gradually transitioning to shear cracks, ultimately leading to shear failure. (3) The variation patterns of AE (acoustic emission) characteristic parameters under the influence of loading rate differ: AE event count, AE energy, and cumulative AE energy show a positive correlation with loading rate, while cumulative AE event count gradually decreases with increasing loading rate. (4) AE characteristic parameters exhibit good correlation with the stress–strain curve and can be divided into four stages. The changes in AE characteristic parameters correspond to the changes in the stress–strain curve. With increasing loading rate, AE signals in the first three stages gradually stabilize, focusing more on the fourth stage, namely the post-peak stage, where the specimens typically experience maximum AE signals accompanying final failure. [ABSTRACT FROM AUTHOR]

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract The weakening of circular tunnels is a global problem that has not been resolved satisfactorily. In the tunnelling process, surrounding rock of circular-tunnel performs a process of “excavating → weakening → continuous excavating → weakening strengthens”. Different rates of excavation affect the stress adjustment of the surrounding rock, and also have an impact on the weakening of a circular-tunnel. An instability failure test was conducted on a circular-tunnel with varying vertical loading rates. The loading rate was utilized as a representative measure for the excavation rate on the site. The results showed that the weakening process of a circular-tunnel can be divided into four distinct phases, hydrostatic pressure (E1), particle ejection (E2), flake stripping (E3), and instability (E4). The ordering of these phases is E3 > E4 > E1 > E2. In the weakening process of a circular-tunnel, the root cause is the original stress level, while the essential factor is the engineering disturbance. A faster vertical loading rate leads to greater stress adjustment, higher strain energy accumulation, and an increased probability of circular-tunnel instability. The presence of a quiet period of AE events in the middle and later phases of flake stripping is a precursory characteristic of circular-tunnel instability. This study has both theoretical and practical significance in terms of revealing the mechanism of circular-tunnel instability and achieving a reasonable arrangement of the circular-tunnel support process.

During deep coal mining processes, periodic mining disturbances cause the neighboring coal strata to bear the effects of cyclic loading and unloading, making it essential to study the mechanical responses and macro-micro failure characteristics of the coal-rock composite structures under different cyclic loads. In this study, three different loading rates were selected to perform uniaxial cyclic compression tests (with simultaneous acoustic emission signal measurement) under two types of cyclic loads, investigating the damage characteristics of coal-rock composites. Based on the principle of energy dissipation, an energy-damage constitutive model for the cyclic loading of composites was constructed and validated with experimental data. The results indicate that the loading rate is directly proportional to the peak strength of the composite specimen, where the peak stress increased by 22.44% and 28.89% for the gradual cyclic loading and unloading path (path I) and the cyclic loading and unloading path (Path II) respectively. The higher the loading rate, the faster the internal crack extension in the specimen, the crushing degree of the coal component in the coal-rock composite specimen is intensified, and the fractal dimension increases subsequently, and the faster the internal crack extension in the specimen becomes. With the increase of the loading rate, the damage along the matrix in the coal fraction increases. The paths with a large span of cyclic gradation (Path I) contribute to stress transfer within the specimen and provide favorable conditions for the development of cracks within the specimen, leading to a higher degree of damage in the corresponding specimen. The consistency between the test curves and the energy-damage constitutive model curves is relatively high, indicating that the proposed energy-damage constitutive model can well describe the deformation behavior of the coal-rock composite specimens during cyclic loading and unloading processes.

The mechanical behavior of the coal body acted upon by varying pressure is very important for the stability analysis of the actual mining face. Based on the designed stress loading path, uniaxial compression tests are performed on coal samples of different coal steps in the presence of various loading rates. The main goal of this investigation is to examine the internal damage and crack evolution characteristics of the coal samples. The results reveal that the ringing number and energy abruptly alter before the peak stress, the resistivity decreases, the damage increases and the internal fracture development of the coal rock intensifies. The low-order coal is essentially damaged in shear after several stages of loading, and the high-order coal is mainly damaged in tension due to the stress concentration caused by the primary cracks, and the fracture rapidly develops along the primary cracks. The obtained results of this study provide a theoretical basis for the design of the protective layer and the control of mining disturbances in the actual working face mining environment. Highlights: Development of an approach of mining disturbed stress loading rate. Assessment of mechanical properties of various coal rank samples subjected to mining disturbed stress environment. Loading rate variations cause sudden changes in the coal rock ringing number, energy, resistivity, and damage. Characteristics of fracture evolution of various coal rank samples during the loading process. [ABSTRACT FROM AUTHOR]

Fiber-reinforced composite materials have emerged as essential solutions for addressing the durability challenges of traditional reinforced concrete, owing to their lightweight nature, high strength, ease of construction, superior tensile capacity, robust corrosion resistance, and excellent electromagnetic insulation properties. This paper delves into the influence of loading rate and fiber bar type on the mechanical characteristics of concrete one-way plates through impact experiments on such plates fitted with glass/basalt fiber bars at varying drop weight heights. The test results reveal a direct correlation between increasing loading rates and escalating damage in fiber-reinforced concrete one-way plates, reflected in the progressive rise in peak deflection and residual displacement at the mid-span of the specimens. Notably, when subjected to higher impact loads, glass fiber-reinforced concrete specimens exhibit amplified deformation and intricate crack formations, consequently diminishing the overall deformation resistance of the plate. Furthermore, glass/basalt fiber-reinforced composites demonstrate notable vibration damping qualities, characterized by substantial residual displacement, minimal rebound, and rapid decay following vibration stimulation. Overall, glass fiber-reinforced one-way plates display marginally superior impact resistance compared to their basalt fiber-reinforced counterparts. [ABSTRACT FROM AUTHOR]

In order to clarify the relationship between the mechanical properties of coal-rock composite and the loading rate and rock–coal strength ratio, uniaxial compression tests were carried out on coal-rock combinations with three different rock–coal strength ratios at four different loading rates. The rock–coal strength ratio is a ratio of the compression strength of rock to the compression strength of coal. The test results indicate that the relationship between the mechanical properties of coal-rock composite and loading rate is influenced by both the strong and weak components in the composite. The peak stress and elastic modulus mainly depend on the weak component, while the peak strain is determined by both the strong and weak components. For peak stress and elastic modulus, when the weak body is the same, the relationship with loading rate is the same, otherwise it is different. The relationship between the mechanical properties of coal-rock combination and is not affected by the loading rate. The weak body in the coal-rock combination is the main body of damage, and the greater the value of , the more severe the damage. At the same time, the failure mode shows a gradual transition from weak body failure inducing strong body failure to only weak body failure. [ABSTRACT FROM AUTHOR]

In recent years, the issue of aircraft icing has gained widespread recognition. The breaking and detachment of dynamic ice can pose a threat to flight safety. However, the shedding and fracture mechanisms of dynamic ice are unclear and cannot meet the engineering needs of ice-shedding hazard assessment. Therefore, studying the fracture toughness of ice bodies has extremely important practical significance. To address this issue, this article uses a centrally cracked Brazilian disk (CCBD) specimen to measure the pure mode I toughness and pure mode II fracture toughness of freshwater ice at different loading rates. The mixed-mode (I–II) fracture characteristics of ice are discussed, and the experimental results are compared and analyzed with the theoretical values of the generalized maximum tangential stress (GMTS) criterion considering the influence of T-stress. The results indicated that as the loading rate increases, the pure mode I toughness and pure mode II fracture toughness of freshwater ice decrease, and the fracture toughness of freshwater ice is more sensitive to the loading rate. In terms of fracture criteria, the theoretical value of the ratio of pure mode II fracture toughness to pure mode I fracture toughness based on the GMTS criterion is in good agreement with the experimental value, while the theoretical value based on the maximum tangential stress (MTS) criterion deviates significantly from the experimental value, indicating that the GMTS criterion considering the influence of T-stress can better predict the experimental results. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mathematics, Mechanics & Computer Science is the property of Al-Farabi Kazakh National University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The material properties of steel and concrete vary depending on the loading rate to which they are subjected. To realistically evaluate the seismic performance of reinforced concrete (RC) columns, it is necessary to simulate the loading rate that structures will experience during seismic events as accurately as possible. Real‐time dynamic testing is preferred over quasi‐static testing for this purpose. On the other hand, the seismic performance of RC columns also depends on the axial force applied to the column. However, due to the large axial stiffness of RC columns, accurately controlling the axial force during the test, particularly in real‐time testing, is challenging. Consequently, only a few component‐level dynamic tests have been conducted for RC columns. This study aims to explore the influence of axial force and loading rate on the seismic performance of RC columns. To this end, both slow and fast cyclic loading tests were conducted on square cross‐section RC columns subjected to four different axial forces. By utilizing a robust actuator control method along with a specially designed load transfer element, the axial force was successfully controlled, while the lateral displacements were imposed on the columns in real‐time. The results include lateral strengths, postyield responses, damage patterns, rebar strains, and their rates, all of which constitute unique experimental data that can contribute to a deeper understanding of the actual seismic response of RC columns. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to study the influence of loading rate on infrared radiation energy of siltstone during loading failure, and quantitatively analyze the change law of infrared radiation energy of siltstone during loading process, the infrared radiation experiments of siltstone under uniaxial compression at different loading rates were carried out. The results show that the peak stress decreases with the increase of loading rate. Under different loading rates, in difference mode, the maximum infrared radiation temperature ΔTmax has a good correspondence with the stress change, which can better reflect the damage of the sample, and the maximum temperature difference of ΔTmax increases by 1.0-1.7 ℃. During the main rupture, cumulative infrared radiant energy increment ΔQ increases slowly with time. There is a power function relationship between ΔQ and mechanical work. With the increase of mechanical work, the cumulative infrared radiation energy increment increases first and then increases slowly. The range of infrared precursor ratio of specimen damage under different loading rates is 0.02-0.285, and decreases with the loading rate.

Abstract Background Running exercise is an effective means to enhance cardiorespiratory fitness and body composition. Besides these health benefits, running is also associated with musculoskeletal injuries that can be more prevalent in individuals with excessive body weight. Little is known regarding the specific effects of overweight and foot pronation on ground reaction force distribution during running. Therefore, this study aimed to investigate the effects of overweight/obesity and foot pronation on running kinetics. Methods Eighty-four young adults were allocated to four experimental groups: non-excessive body weight/non-pronated feet; non-excessive body weight/pronated feet; overweight or obesity/ non-pronated feet and overweight or obesity/pronated feet. Biomechanical testing included participants to run at ~ 3.2 m/s over an 18-m walkway with an embedded force plate at its midpoint. Three-dimensional ground reaction forces were recorded and normalized to body mass to evaluate running kinetics from 20 running trials. Test–re-test reliability for running speed data demonstrated ICC > 0.94 for each group and in total. Results The results indicated significantly lower vertical impact peak forces (p = 0.001, effect size = 0.12), shorter time to reach the vertical impact peak (p = 0.006, effect size = 0.08) and reduced vertical loading rate (p = 0.0007, effect size = 0.13) in individuals with excessive body weight (overweight or obesity/non-pronated feet group and overweight or obesity/pronated feet) compared with individuals non-excessive body weight (non-excessive body weight/non-pronated feet and non-excessive body weight/pronated feet). Moreover, the excessive body weight groups presented lower peak braking (p = 0.01, effect size = 0.06) and propulsion forces (p = 0.003, effect size = 0.09), lower medio-lateral loading rate (p = 0.0009, effect size = 0.12), and greater free moments (p = 0.01, effect size = 0.07) when compared to the non-overweight groups. Moreover, a significant body mass by foot pronation interaction was found for peak medio-lateral loading rate. Non-excessive body weight/pronated feet, excessive body weight/non-pronated feet and excessive body weight/pronation groups presented lower medio-lateral loading rates compared to non-excessive body weight/non-pronated feet (p = 0.0001, effect size = 0.13). Conclusions Our results suggest that excessive body weight has an impact on ground reaction forces during running. We particularly noted an increase in medio-lateral and torsional forces during the stance phase. Individuals with excessive body weight appear to adapt their running patterns in an effort to attenuate early vertical impact loading.

This paper developed a one-dimensional multiphase model to analyze the cold start behavior of fuel cell, focusing on the effects of various parameters such as loading rates, maximum loading current densities, and coolant flow rates. The findings reveal that the loading rate significantly influences the ice volume fraction and the duration required for cold start, while exerting a lesser effect on voltage and the voltage variation. Cold start fail at maximum loading current densities below 0.4 A cm−2 due to a heating rate insufficient to outpace the rate of ice formation. However, as the maximum loading current density surpasses this threshold, successful start-ups are achieved, although the benefits to voltage, start-up time, and voltage variation diminish with increasing current density. The coolant flow rate primarily impacts the temperature distribution’s uniformity across individual cells, with negligible effects on overall cold start performance. Utilizing Gaussian process regression models for training and prediction reveals that elevating the loading rate and maximum loading current density can effectively mitigate ice formation. The relationship between these variables and performance metrics such as voltage, start-up time (The time required from the loading start to the successful start-up), and voltage variation is characterized by an initial increase followed by a subsequent decrease as the loading rate climbs. Conversely, the influence of the maximum loading current density on these metrics is comparatively modest.

The relationship between internal loading dose and low-back injury risk during lifting is well known. However, the implications of movement parameters that influence joint loading rates—movement frequency and speed—on time-dependent spine loading responses remain less documented. This study quantified the effect of loading rate and frequency on the tolerated cumulative loading dose and its relation to joint lifespan. Thirty-two porcine spinal units were exposed to biofidelic compression loading paradigms that differed by joint compression rate (4.2 and 8.3 kN/s) and frequency (30 and 60 cycles per minute). Cyclic compression testing was applied until failure was detected or 10,800 continuous cycles were tolerated. Instantaneous weighting factors were calculated to evaluate the cumulative load and Kaplan–Meier survival probability functions were examined following nonlinear dose normalization of the cyclic lifespan. Significant reductions in cumulative compression were tolerated when spinal units were compressed at 8.3 kN/s (P <.001, 67%) and when loaded at 30 cycles per minute (P =.008, 45%). There was a positive moderate relationship between cumulative load tolerance and normalized cyclic lifespan (R2 =.52), which was supported by joint survivorship functions. The frequency and speed of movement execution should be evaluated in parallel to loading dose for the management of low-back training exposures. [ABSTRACT FROM AUTHOR]

The cracking problem of asphalt concrete panels is a crucial consideration in the design of hydraulic asphalt concrete seepage control bodies. Panels experiencing uneven rises or falls of water levels during impoundment may exhibit loading rate effects. Investigating the fracture toughness value of asphalt concrete under varying loading rates is essential. This study employs a statistical method to calculate the fracture index KIC, using the semi-circular bending test (SCB) to examine the effect of loading rates on the Type I fracture mode of hydraulic asphalt concrete. The data are analyzed using the two-parameter Weibull distribution curve, offering insights into the minimum number of KIC test specimens. The results indicate an increase in KIC with loading rate, with greater data dispersion at faster rates. The Weibull distribution curve successfully fits the fracture behavior under different loading rates, providing valuable predictions. This study estimates the minimum number of SCB test specimens to be nine, based on a confidence level of 0.95 and a relative deviation not exceeding 5%. [ABSTRACT FROM AUTHOR]

In the process of mining, there are rocks affected by cyclic disturbances, which have significant effects on the mechanical properties of rocks. To understand the loading rate effect of rocks under different cyclic loading and unloading methods,this paper carries out constant lower Unit cyclic loading and unloading, variable lower Unit cyclic loading and unloading tests on sillimanite specimens with different loading rates, comparatively analyzes the deformation characteristics, the energy evolution law and the destructive characteristics of the specimens under the two cyclic loading and unloading methods with different loading rates. The test results show that the peak strength and residual deformation of the specimen have different acceleration rate effects, but the peak strength is improved compared with the conventional uniaxial compression test; WITH the increase of the loading rate, the input energy, elastic energy and dissipation energy of the specimen in all stages show an increasing trend, but with some differences in the form of manifestation; the destruction of the specimen and IS morphology show the acceleration rate effect, and the degree of destruction is intensified with the increase of the loading rate. [ABSTRACT FROM AUTHOR]

As the latest development of gravity installed anchors (GIAs), the OMNI-Max anchor has drawn much attention from worldwide due to its unique behavior in the seabed. The pullout capacity of OMNI-Max anchors is a key index in engineering. However, most of the relevant studies were carried out under a quasi-static condition, which do not actually meet the installation and operation requirements. In practice, the anchor may be subjected to both long-term and short-term sharp loading during mooring. As an important environmental variable, it is essential to evaluate the effect of loading rate on the pullout capacity. Since the bearing capacity of OMNI-Max anchors is affected by many factors, it is also essential to explore systematically the coupling effects of the loading rate and other factors, including the anchor embedment depth, the anchor orientation, the bearing area, the loading angle, and the soil strength. Based on the coupled Eulerian-Lagrangian (CEL) technique, numerous analytical cases are designed and calculated by the large deformation finite element (LDFE) method. The loading rates span four orders of magnitude from the quasi-static velocity to 10 m/s (about one anchor length per second), covering a wider range in pulling out of GIAs. The end-bearing capacity factor changes remarkably with the pullout velocity for OMNI-Max anchors, and the increase can even reach more than twice of that in a quasi-static condition. As a result, a succinct explicit expression is constructed in terms of the loading rate and multiple factors, which can be effectively utilized to calculate the end-bearing capacity factor of OMNI-Max anchors in clay under complex conditions. [ABSTRACT FROM AUTHOR]

Due to viscoelastic characteristics, the strength values of the high-modulus asphalt mixtures (HMAM) obtained under different conditions (temperatures, loading rates, and stress states) are quite different, and the serving conditions of asphalt pavements are also varied. Thus, the strength under fixed conditions cannot reflect the mechanical performances of materials under real serving conditions, which leads to inaccuracies in the asphalt pavement structural design. To develop a precise strength evaluating method for high-modulus asphalt mixtures, the strength tests of high-modulus asphalt mixtures were implemented under different conditions (temperatures, loading rates, and stress states) in this study. The test results indicated that for each stress state, the variation of strength with loading rates under different temperatures can be characterized by power functions, and the variation of strength with temperatures under different loading rates can be characterized by exponential functions. The uniform characterizing model of strength under different conditions was established through the dimensionless method and the sigmoidal function. With the effects of temperature, loading rates, and stress states included, the strength obtained can better reflect the mechanical performances in actual pavement serving conditions. The research results contribute to the improvement of the structural resistance design of the asphalt pavement with high-modulus asphalt mixtures. [ABSTRACT FROM AUTHOR]

Expanded polypropylene (EPP) foam has been widely recognized as an energy absorbing material, and it is routinely used for variety of industrial applications. However, EPP foam has a relatively limited scope in the construction industry, especially for load-bearing applications. To address this aspect, the mechanical behaviour of EPP foam was examined under unconfined conditions in this study, and the effects of different preloading/precompression strain histories (5% to 60%) on the stress-strain response and strain energy characteristics of EPP were evaluated. Additionally, the stress-strain recovery behaviour of EPP foam having different preloading histories was also studied while considering the effects of recovery time after preloading (0 to 28 Days). The results suggest that EPP foam subjected to different preloading histories has identical patterns of stress-strain response to other conventional closed-cell polymeric foams, such as expanded polystyrene (EPS) foam, and EPP can adequately be used for load-bearing applications under the recommended design limits. Furthermore, noticeable recovery in the stress-strain response of EPP was also witnessed during the initial 14 days after preloading. Based on these findings, it is anticipated that the promising stress-strain recovery characteristics of EPP foam enable it to be reused, even after experiencing large in situ deformations. [ABSTRACT FROM AUTHOR]

In the field of rock engineering, complexity of stress environment is an important factor affecting its stability. Thus, in view of fracture mechanism of rock under different loading rates within the scope of quasi-static strain rate, four groups of uniaxial compression tests with different strain rates were carried out on sandstone specimens, and strength, deformation, failure modes and acoustic emission characteristics of specimens were compared and analyzed. Furthermore, the fracture mechanism was discussed from the perspective of fracture characteristics based on fractal dimension, crack propagation law inverted through acoustic emission b-value, and micro fracture morphology. The results showed that as the strain rate increased from 10 to 5 s-1 to 10-2 s-1, the fractal dimension of rock fragments increased, and the fractal dimension of rock fragments increased by 9.66%, 7.32%, and 3.77% successively for every 10 times increase in strain rate, which means that the equivalent size of fragments was getting smaller, and the fragmentation feature was becoming increasingly prominent. The crack propagation process based on acoustic emission b-value showed that with the increase of loading rate, the specimen entered the rapid crack propagation stage earlier, in order of 68%, 66%, 29%, and 22% of peak stress. Moreover, the microscopic fracture morphology showed that with the increase of loading rate, transgranular phenomenon was clear, and the fracture morphology changed from smooth to rough. That meant that the fracture of sandstone rock at high loading rates was mainly caused by the propagation of large cracks, which was different from the slow process of initiation, convergence and re-propagation of small cracks at low strain rates. Due to warm and humid air currents of the Indian Ocean and the southwest monsoon, the Palong Zangbo catchment in southeastern Tibet has developed oceanic glaciers in the valley, and the activity of glacial debris flows has been gradually intensified under neotectonic activity, frequent earthquakes, climate change, and extreme rainfall. In this paper, the topographic and morphological data of the debris flow basin, the dynamic evolution characteristics of glaciers and glacial lakes were analyzed by using multisource long-term series of remote sensing images. Simultaneously, the distribution of moraines and landslide sources were extracted based on satellite image. In addition, climate change in the study area was analysed using temperature and rainfall data from the last 40 years, revealing that the average temperature in the study area from May to October presented a fluctuating tendency as a whole, especially after 2013, when the temperature gradually increased. As these temperature changes led to continuous melting of the glaciers in the study area, the glacier area decreased from 8,300 km2 in 1988-4,584 km2 in 2019, which decreased nearly 45%. However, the number and area of glacial lakes in the study area gradually increased under a power-law trend, which further led to a significant increase on the possibility of glacial lake rupture in the study area. Due to the joint effects of earthquakes, glacier melting and glacial lake collapse, the debris flows in the study area were well developed, and a total of 122 debris flows were found with varying channel lengths, areas and material sources. Importantly, the characteristics of the glaciers, glacial lakes and climate change in the study area have indicated that the glaciers have retreated, the number of glacial lakes has increased, and the risk of debris flow in this basin will increase in the future. Therefore, it is necessary to strengthen monitoring and early warnings on floods due to glacial lake collapses and debris flows in the study area to improve the risk management of debris flows and floods and the prevention and mitigation of disasters. [ABSTRACT FROM AUTHOR]

In view of the non-uniqueness of modulus selection and the mismatch among the values of various mechanical parameters of the same material in the current asphalt pavement design, typical pavement materials, asphalt mixture (AC), and cement stabilized macadam (CSM) were selected to perform unconfined compressive, direct tensile, bending, and splitting tensile tests. Then, the quantitative matching relationships among the mechanical parameters were established considering the velocity dependence and the different properties of tension and compression. Moreover, the superiority–inferiority of the four test methods was also evaluated by analyzing the stability and change law of test data and the specimens force characteristics. The results show that the difference in tension and compression of strength and modulus was the inherent attribute of the materials, which leads to the non-uniqueness of the mechanical parameters. The unconfined compressive and direct tensile tests are suitable methods to obtain mechanical parameters of pavement materials. The ratio of the direct tensile strength (modulus) to unconfined compressive strength (modulus) of AC decreases (increases) with the loading rate, while those of CSM shows an opposite regular pattern, and these above ratios of the two pavement materials tend to be a fixed value at higher loading rates. This research can provide a reference for the scientific selection and proper value of mechanical parameters in asphalt pavement design. [ABSTRACT FROM AUTHOR]

In order to study the effects of loading rate and freeze-thaw cycles on the dynamic splitting characteristics of sandstone, static and dynamic splitting tests with different loading rates were conducted on sandstone subjected to 0, 25, 50, 75 and 100 freeze-thaw cycles, and the static and dynamic tensile strength of freeze-thaw sandstone, as well as the change law of dissipation energy under impact load were discussed. The results show that the static and dynamic tensile strength, the P-wave velocity and the mass loss rate of freeze-thaw sandstone deteriorate with an increase in the number of freeze-thaws cycles. The dynamic strength increase factor (DIF) increases with the increase of freeze-thaw cycles and loading rate, and a higher degree of the freeze-thawing damage in sandstone results in a more significant increase in DIF with loading rate. The dynamic tensile strength prediction model based on freeze-thaw damage and loading rate can reflect the strength change of sandstone effectively. The greater the freeze-thaw damage of sandstone, the faster the change of dynamic tensile strength with loading rate. The dissipation energy under impact load decreases with the increase of freeze-thaw cycles and increases with higher loading rate. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Northeastern University (Natural Science) is the property of Dongbei Daxue Xuebao and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)