Mechanical Behavior Evolution Research Articles

Experimental and numerical investigation on the shear behavior and damage mechanism of segmental joint under compression-shear load

The segment dislocation at circumferential joints severely impacts on the structural safety of shield tunnels during construction and operation. Especially for the underwater tunnel with a super-large cross-section, the circumferential joint usually consists of oblique bolts and distributed mortises and tenons to control the dislocation. Given this, a series of full-scale loading tests of the circumferential joint is carried out based on Jinan Yellow River Tunnel, and a three-dimensional refined numerical model with concrete damage plastic (CDP) constitutive is also established to reveal the condition of stress and damage. The deformation process of joints, the stress of bolts, and the damage characteristics of mortises and tenons are investigated through the full-scale tests and numerical simulation. Moreover, the mechanical behavior and damage evolution of circumferential joint has been revealed under compression-shear loads. Besides, the influence of mortises and tenons, bolts on the shear resistance of joints is unraveled. The results show that the deformation process of the circumferential joint can be divided into three stages under the ordinal shearing loading scenario (OSLS) and reverse shearing loading scenario (RSLS). The bolt plays an important bearing role under OSLS and the bolt is in an unstressed state under RSLS, which makes the shear stiffness and shear capacity of the joint under OSLS larger than that under RSLS. The tenon and bolt hole damage presents local concrete crushing, while the damage of mortise occurred with concrete spalling. Compared with bolts, the mortises and tenons can significantly improve the shear stiffness and the ultimate bearing capacity of circumferential joints.

Impacts of bedding angle and cementation type of bedding planes on mechanical behavior of thin-layer structured bedded rocks under uniaxial compression

To investigate the mechanical behavior and crack evolution properties of the anisotropic bedded rocks, a series of uniaxial compression tests were conducted using bedded limestone, phyllite, and shale specimens, and the bedding angle α of specimens was designed as 0°, 15°, 30°, 45°, 60°, and 90°. The acoustic emission (AE) and digital image correlation (DIC) techniques were applied to monitor the crack evolution mechanism. The cementation types of bedding planes were also different, which greatly affected the mechanical properties of bedded rocks. In this study, the cementation types of bedding planes for limestone, phyllite, and shale were defined as embedded cementation, oriented cementation, and cracked cementation, respectively. The experimental results showed that with the increase of the α, the peak strength σucs, elastic modulus E, AE hit rate, cumulative AE hit and cumulative AE energy all exhibited a decreasing firstly and then increasing trend, and all showed obvious anisotropy. A novel trigonometric strength criterion for bedded rocks was developed. The fluctuation of the b-value indicated that the propagation of the internal micro-cracks was unstable, and showed an overall downward trend. Meanwhile, a tensile and shear crack classification criterion combining the AE parameters, clustering idea and genetic algorithm was proposed, and then the rational dividing line of tensile and shear cracks was determined in AF-RA maps. The α and cementation types both affected the failure mode of bedded rocks. For limestone with α = 0°– 90°, the longitudinal splitting, forming approximate vertical macro tensile cracks, was the primary failure mode, and local shear slipping along the bedding plane occurred in the specimens with α = 30°– 60°. For phyllite and shale, when α≤ 30°, the inclined macro-cracks were not along the bedding planes but showed a shear-dominated failure mode. When 45° ≤α≤90°, the main macro-cracks were along the bedding planes, and some macro-sub cracks penetrated the bedding planes in shale, showing shear-dominated failure for specimens with 45°≤α<90° and tensile-dominated failure for specimens with α=90°. The method of rating scores corresponding to the uniaxial compressive strength in RMR has been improved and an optimization method of the revised rating scores of bedded rocks in different situations considering α and σucs has also been proposed.

Macroscopic mechanical behavior and microstructural evolution of compacted loess in the Chinese Loess Plateau

Understanding the mechanical behavior of compacted loess is of great significance to engineering construction on the Loess Plateau. To gain an in-depth knowledge of the variations in compressibility, shear strength and microstructure of compacted loess at different dry densities and water contents, a series of macro and microscopic tests were carried out on the loess samples, including oedometer compression tests, direct shear tests and scanning electron microscope imaging. The pore properties of loess in microscopic images were investigated using the particle (pores) and cracks analysis system. The relationship between pore microscopic indicators and mechanical parameters was explored by multivariate statistical analysis. The results show that the compression coefficient of compacted loess decreases with increasing dry density, of which trend is more significant at high water content. Both cohesion and internal friction angle decrease with increasing water content, but the former is more sensitive to changes in soil moisture. Besides, the evolution sequence of compacted loess structure is basically overhead-mosaic-flocculation with the increase of compactness and saturation. The difference is that with the compaction, the pores in the loess sample change from macropores into mesopores and then to small pores, and the directional distribution and morphological complexity of the pores weakens; while with the humidification of the loess sample, small pores and macropores transform into mesopores, and the pores are more oriented and more complex in shape. During this process, the micropore content changes are weak. Moreover, mesopores content and pore fractal dimension have a positive effect on compressibility, while micropores content and orientation probability entropy have a positive effect on shear strength.

Mechanical behaviour and fracture evolution of coal specimens containing an over‐excavated hole: Experimental study and numerical modelling

AbstractUtilising a series of mechanically over‐excavated cavities along borehole is a novel technique for enhancing the permeability of soft coal seams and, consequently, gas drainage. The evolution of cracks induced by a wide range of pressure‐relief around an over‐excavated hole is intrinsically complex. In this study, the mechanical behaviour and crack evolution of the specimens containing an over‐excavated hole under uniaxial compression loading were studied by experimental and 3D numerical simulation. The results indicated that the peak strength and elastic modulus of the specimens gradually decrease with increasing cavity diameter and length, which is also verified by the numerical simulation. The inclusion of cylindrical cavities in over‐excavated holes results in reduced crack initiation stress and a greater degradation of peak stress and elastic modulus, despite having an equivalent volume to the ellipsoidal cavity. This is likely attributed to the difference in stress concentration between the cylindrical and ellipsoidal cavities. The crack propagation process can be classified into four stages based on the acoustic emission (AE) event counts, initial crack compaction, stable crack propagation, unstable crack propagation and post‐peak failure stage. The two AE indices, rise angle and average frequency value, demonstrated that the failure is dominated by tensile crack and gradually transformed to shear crack. Stress redistribution is essential in the initiation and propagation of cracks. Tensile stress concentration leads to cracks forming at the top and bottom of the hole, which propagate in the direction of loading. Compressive stress concentration results in shear cracks forming at the left and right sides of the hole, which propagate diagonally. The failure pattern of the specimen is ultimately determined by a combination of tensile and mixed crack propagation. The experimental and numerical results contribute to a deeper understanding of the crack evolution mechanism of coal seams with over‐excavated holes.

Study on the mechanical properties of unloading damaged sandstone under cyclic loading and unloading

To reveal the mechanical properties of rocks under stress disturbance and unloading confining pressure, conventional triaxial compression tests, triaxial compression tests on unloading damaged sandstone, and cyclic loading and unloading tests on unloading damaged sandstone were conducted. Then, the evolutionary characteristics of dissipated energy in sandstone under cyclic loading and unloading were explored, and damage variables were proposed. The crack development characteristics were analyzed from a microscopic perspective. The study results reveal that: (1) the sandstone exhibits obvious brittle failure under different stress paths, and the macroscopic failure mode is dominated by shear failure. As the number of cycles increases, the load-bearing capacity, elastic modulus, and deformation modulus of the sandstone will be significantly reduced if it suffers greater unloading damage. (2) The cyclic action in the early stage inhibits the development of the internal fracture. However, the inhibitory effect is significantly reduced for specimens with larger unloading quantities. The damage variable in the cyclic loading and unloading is about 50.00% of that in the unloading, indicating that unloading confining pressure is the dominant factor for specimen failure. (3) The extension of microcracks within the sandstone is dominated by intergranular cracks, and the number of cracks increases with the increase of unloading quantity. After cyclic loading and unloading, the structure becomes looser. The test results deepen the understanding of rock mechanical behavior and fracture evolution under cyclic loading and can provide a basis for structural stability improvement under stress disturbance and unloading confining pressure.

Research on Algorithm of Corrosion Fatigue Damage Evolution of Stay Cables and Structural Mechanical Behavior with Cable Fracture

From the point of view of material multiscale analysis, the deterioration of the fatigue properties of the cable is due to the micro-damage inside the strand. To describe the damage failure process of the cable as accurately as possible, many micro damage details need to be implanted in the strand model. However, with the increase of the number of wires in the cable body, this modeling method will produce a large number of elements in the finite element model of the stay cable, which makes the calculation cannot be completed iteratively. Based on this, a time-step adaptive simulation method for corrosion fatigue damage evolution of stay cables was proposed in this paper. In this method, the corrosion fatigue damage evolution model was implanted in the local part of the strand model, and a damage variable was used to comprehensively consider the evolution behavior of distributed micro-damage in the strand, which satisfies the calculation accuracy and realizes the simulation of the whole process of fatigue deterioration of the stay cable, greatly improving the calculation accuracy and convenience. Then taking an in-service cable-stayed bridge as an example, the stress of the main beam and the local spatial stress of the main beam under the special condition of the cable damage failure were studied by combining the rod model with the local model, which provides data reference for the replacement of the cable of the cable-stayed bridge with a long construction life.

Effect of drying-wetting cycles on pore characteristics and mechanical properties of enzyme-induced carbonate precipitation-reinforced sea sand

Enzyme-induced carbonate precipitation (EICP) is an emanating, eco-friendly and potentially sound technique that has presented promise in various geotechnical applications. However, the durability and microscopic characteristics of EICP-treated specimens against the impact of drying-wetting (D-W) cycles is under-explored yet. This study investigates the evolution of mechanical behavior and pore characteristics of EICP-treated sea sand subjected to D-W cycles. The uniaxial compressive strength (UCS) tests, synchrotron radiation micro-computed tomography (micro-CT), and three-dimensional (3D) reconstruction of CT images were performed to study the multiscale evolution characteristics of EICP-reinforced sea sand under the effect of D-W cycles. The potential correlations between microstructure characteristics and macro-mechanical property deterioration were investigated using gray relational analysis (GRA). Results showed that the UCS of EICP-treated specimens decreases by 63.7% after 15 D-W cycles. The proportion of mesopores gradually decreases whereas the proportion of macropores increases due to the exfoliated calcium carbonate with increasing number of D-W cycles. The microstructure in EICP-reinforced sea sand was gradually disintegrated, resulting in increasing pore size and development of pore shape from ellipsoidal to columnar and branched. The gray relational degree suggested that the weight loss rate and UCS deterioration were attributed to the development of branched pores with a size of 100–1000 μm under the action of D-W cycles. Overall, the results in this study provide a useful guidancee for the long-term stability and evolution characteristics of EICP-reinforced sea sand under D-W weathering conditions.

Understanding the microstructure evolution and mechanical behavior of titanium alloy during electrically assisted plastic deformation process

Titanium alloys are widely used in aerospace, petrochemical, and automobile industry due to their outstanding mechanical properties. However, the formability/plasticity of most titanium alloys at room temperature is relatively poor, and a large amount of energy is needed to manufacture them. In this study, the electrically assisted plastic deformation (EAPD) process is explored in a titanium alloy – TC11, to investigate how it can be used to enhance its formability/plasticity. A systematic study was conducted on the mechanical behavior and microstructure evolution of the TC11 during the EAPD process under different current densities (5–15 A/mm2) and strain rates (10−3-10−1s−1). The effects of the pulse current on the yield strength and microstructure of the titanium alloy TC11 are investigated. We found that the yield strength of the TC11 titanium alloy decreases with the increment of current density and the decrease of strain rate, suggesting that pulse current can improve the formability/plasticity of TC11 titanium alloy while reducing energy consumption during manufacturing. With the help of EBSD, TEM, and HAADF-STEM, we were able to characterize the phases refinement, dislocation annihilation, and element diffusion in the alloy. This phenomenon was explained by the recrystallization of the β phase during the EAPD process. Furthermore, the constitutive equations for the TC11 titanium alloy during the EAPD process have been formulated. The deformation stress predicted by the constitutive model agrees well with the experimental data. This study provides valuable insight into the mechanical behavior and microstructure evolution of the TC11 titanium alloys during EAPD.

Irradiation-enhanced superficial modification and evolution of mechanical behavior in TaTiNbZr refractory high entropy alloy films exposed to low energy helium plasma

In this work, TaTiNbZr refractory high entropy alloy (RHEA) films constructed with nano-crystalline and amorphous composite structures were irradiated by helium (He) plasma with a fixed flux of 5 × 1022 m−2·s−1 under bias-voltage driven plasma energy (0–70 eV) to systematically explore the evolution of morphological modification and mechanical properties. The results indicated that the RHEA exhibited composite structures after He plasma irradiation, and the irradiation-enhanced surface blisters were strongly dependent on He plasma energy. After exposure to He plasma, the size and density of blisters on the surface of RHEA films gradually increased with the enhancement of plasma energy, these blisters originated from the formation of bulges underneath the surface which were induced by the large-sized bubbles. Some blister bursts were initiated at a critical energy of 50 eV (irradiation temperature was 600 K). Non-obvious superficial sputtering can be observed for the RHEA films irradiated at energy less than 50 eV. At the He plasma energy of 70 eV, cracks and abundant blister exfoliation were produced on the RHEA surface due to the synergistic effect of enhanced energy and irradiation temperature (650 K). Surface sputtering and the thermal diffusion-driven mass flow were induced by He plasma due to the sputtering threshold energies in Ti and Zr elements than that of Ta and Nb elements, which were responsible for the growth of fiber-like structures on the surface of RHEA film as the energy was fixed at 70 eV. Moreover, the maximum hardening ratio of 21.4% was revealed from the TaTiNbZr RHEA nano-film irradiated at plasma energy of 50 eV, the role of plasma energy on the evolution of mechanical properties, and the corresponding mechanisms in response to irradiation damage were also discussed in detail.

Mechanism of strain hardening of magnesium single-crystals: Discrete dislocation dynamics simulations

Poor ductility heavily limits the industrial application of magnesium (Mg) alloys, and pyramidal dislocations are an important deformation mode for ductility enhancement. In this work, discrete dislocation dynamics (DDD) simulations were performed to study the mechanical behavior and dislocation evolution of Mg single-crystals compressed along c-axis. Especially, basal-transition and cross-slip algorithms of pyramidal <c+a> dislocations were proposed and introduced in the DDD method. Simulation results show that basal-transition is an important mechanism for the strong strain hardening observed during c-axis compression of Mg single-crystals. Since the basal-transition events are thermally activated, increasing temperature leads to a high strain hardening rate. During the deformation, the <c+a> dislocations on first-order pyramidal planes mostly cross slip onto second-order pyramidal planes and few are transited onto basal planes, while <c+a> dislocations on second-order pyramidal planes are mostly transited onto basal planes directly. In addition, the basal-transition behavior is an important reason for the formation of dislocation loops and dislocation steps observed in experiments. The current work provides new mechanisms for the pyramidal dislocations, which are significant for understanding the behaviors of pyramidal dislocations and ductility enhancement of Mg alloys.

Mechanical Behavior and Damage Evolution of a Fabricated Rectangular Tunnel with a Mortise-and-Tenon Joint under Internal Explosion

A new mortise-and-tenon joint for a fabricated rectangular tunnel is designed in this study. To explore the damage evolution of a fabricated rectangular tunnel with a mortise-and-tenon joint under internal explosion, a refined numerical model is established by using Abaqus finite element software. The sensitivity of the explosion resistance of a rectangular tunnel to different trinitrotoluene (TNT) equivalents, concrete strength grades, scaled distances, and types of joints is analyzed. The spatiotemporal effect and damage characteristics of the fabricated rectangular tunnel after a central explosion are discussed. Finally, the deformation characteristics of the tunnel corner are quantified by defining a tunnel deformation angle. The results show that the tunnel is more sensitive to the explosion equivalent and less sensitive to the concrete strength grade, and the tunnel roof is highly sensitive to TNT at different distances. The damage of the fabricated rectangular tunnel under an explosion wave has significant spatiotemporal evolution characteristics. The roof and floor of the tunnel are first impacted by explosion, and their reflection on the explosion wave will significantly enhance the explosion effect. The joint of the prefabricated tunnel has small stiffness and large flexibility, and the reflection enhancement effect on the shock wave is weak. The impact of explosive waves results in tensile stresses on the outside of the roof and floor of the tunnel and on the connection of the midpartition, where the explosion resistance is weak. The tunnel deformation angle is used to quantify the deformation damage characteristics of the tunnel. The results show that the safety height of the vehicle in the tunnel should be controlled within 3.8 m. The current research provides some valuable information for the future antiexplosion design and evaluation of the prefabricated frame tunnel.

Study of mechanical characteristics and damage mechanism of sandstone under long-term immersion

The microscopic pore structure of sandstone gradually changes under long-term immersion, resulting in dynamic changes in the mechanical and damage properties of sandstone, which brings challenges to maintain the long-term stability of underground engineering. In this paper, the evolution of pore structure and mechanical behavior of sandstones at different immersion times (0d, 3d, 30d, 90d, 180d and 360d) is studied. A series of physico-chemical experiments and uniaxial compression tests (with simultaneous acquisition of acoustic emission (AE) signals) are conducted to explore the weakening mechanism and failure mode of sandstones during long-term immersion. The results show that long-term immersion has a significant effect on the pore structure and mechanical behavior of sandstones. Various physical parameters indicate that the change in the pore structure of a sandstone with increasing immersion time can be divided into two stages, namely the swelling stage of clay minerals (saturation process) and the corrosion stage of potassium feldspar (long-term immersion process). The variation of pH value and K+ concentration in soaking solution can provide a basis for the division of pore structure stages. From the perspective of mechanical behavior, the uniaxial compressive strength (UCS) and cumulative AE counts of a sandstone decrease by 83% and 96.8% respectively after 360 d of immersion, with enhanced plastic characteristics. The macroscopic failure mode of a sandstone changes from combination of shear and tensile crack surfaces to a single shear crack surface. Based on the results of physico-chemical experiments and mechanical tests, it can be assumed that microcracks in long-term immersion sandstones are more prone to develop along weakened cementation surfaces. Under the effect of stress, corrosion pores formed by potassium feldspar provide space for the rotation and movement of quartz grains, making it more prone to shear slip. The study results enhance our understanding of weakening mechanisms at long-term immersion and provide a basis for assessing the long-term stability of underground engineering.

Cracking Behavior of Atmospheric Plasma-Sprayed 8YSZ Thermal Barrier Coatings during Thermal Shock Test

The failure of plasma-sprayed thermal barrier coatings (TBCs) during service is usually related to the cracking behavior. In this study, plasma-sprayed TBCs were prepared with two kinds of agglomerated sintered yttria-stabilized zirconia (YSZ) powders with different particle sizes. The evolution of mechanical properties and crack propagation behavior of the coatings during the whole life stage were studied by a thermal shock test. The effect of powder particle size on the cracking behavior of the TBCs during thermal shock was analyzed from the aspect of pore structure, mechanical properties, and stress state of the coatings. The crack propagation and coalescence in the direction parallel to the substrate in the coating is the main factor leading to the spalling failure of the coating during thermal shock. Although the coating prepared by fine YSZ has higher fracture toughness, the lower strain tolerance will increase the cracking driving force on the crack tip of the coating during thermal shock, and the cracks in the coating propagate merge at a faster rate during thermal shock. The larger porosity and pore size of the coating prepared by coarse YSZ help the coating suffer less thermal stress during thermal shock. Although the existence of pores reduces the fracture toughness of the coating to a certain extent, the increase of strain tolerance reduces the crack growth rate in the coating, so the coating has a longer life.

Full-scale test and numerical modeling on deformation and damage behavior of segmental joints under ultimate compression-bending load

Investigating the deformation and damage behavior of segmental joints is of great significance for design optimization safety evaluation of shield tunnel. In this study, the full-scale tests of segmental joint under compression-bending load were carried out. A three-dimensional numerical calculation model with concrete damaged plasticity (CDP) constitutive was developed, of which the accuracy was validated by the full-scale test. The mechanical behavior and damage evolution process of the segmental joint, the strain of the bolt and the reinforcement are investigated. The experimental and numerical results revealed that the bending moment-rotational angle curves of segmental joint can be divided into four stages under positive bending moment and three stages under negative bending moment. The difference is mainly due to that the waterproof structure is only set outside the segmental joint. The maximum stress of the bolt occurred in the front of the thread rather than the corresponding location of the joint surface. Compared with Von Mises stress criterion, the method of judging the yield of bolt by the ultimate elastic strain usually adopted in the full-scale test is conservative. The bolt yields under negative bending moment later than that under positive bending moment, and the difference is about 49.8%. The maximum strain of the reinforcement is located at the first stirrup near the joint surface. The strain of the reinforcement at the sleeve side is obviously larger than that at the hand hole side under positive bending, while the opposite is true under negative bending.

Experimental Study on Mechanical Behavior and Energy Evolution Characteristics of Gas-Filled Deep Coal under Cyclic Loading

To study the mechanical behavior and energy evolution law of gas-filled deep coal, conventional triaxial compression experiments under different confining pressure and gas pressure conditions and cyclic loading and unloading experiments under different gas pressures were carried out. The failure characteristics and mechanical parameters evolution of two loading modes were analyzed. In addition, the energy density and ratio evolution law under cyclic loading was revealed, and based on these findings, an attempt was made to depict the relation of cumulative dissipated energy density and volumetric strain by fitting the experimental data. The results indicated that failure of coal is expressed as a single shear surface under conventional compression, while under cyclic loading mode, coal behaves with multi-fracture crushing failure. Mechanical parameters showed a trend of decay with increasing gas pressure, and that cyclic loading and unloading increases the bearing capacity of coal by 8–38%. The dissipated energy density and ratio grew significantly when coal entered the yield stage. In the compaction stage, the cumulative dissipated energy density rose with volumetric strain in the form of an exponential function, and it increased with relative volumetric strain as a power function.

True Triaxial Experimental Study of Anisotropic Mechanical Behavior and Permeability Evolution of Initially Fractured Coal

True Triaxial Experimental Study of Anisotropic Mechanical Behavior and Permeability Evolution of Initially Fractured Coal

Mechanical behaviour and microstructure evolution of wrought magnesium alloys under dynamic compression loading: a review

As one of the lightest structural metals, magnesium alloys have attracted enormous attention owing to its attributes of high specific strength and specific stiffness, superior damping capacity and shock absorbency and so on. The wide application fields of wrought magnesium alloys include aerospace, transportation, and so on. It is critical to understand the correlation between dynamic mechanical response and microstructure evolution of wrought magnesium alloys in stringent impact service environment. Split Hopkinson pressure bar has become the universal and common apparatus to investigate the dynamic compression mechanical behaviour of materials under impact loading state. The recent development of dynamic (high strain rate) compression mechanical behaviour and microstructure evolution of common wrought magnesium alloys are summarized in this paper. The research directions in the future are also suggested.

Effects of wetting and drying cycles on the mechanical behaviour of Lightweight Cemented Soils

An experimental investigation on the durability of Lightweight Cemented Soils (LWCS) after wetting and drying cycles was developed, focusing on the evolution of their mechanical response. Wetting and drying cycles were performed in climatic chamber to test their mechanical performance as function of number of cycles and the environmental conditions (50% and 90% of Relative Humidity). Unconfined compression tests and triaxial tests were performed on treated specimens after cycles in dry state. Suction of LWCS samples was measured after mechanical tests. Test results show that the wetting-drying cycles and the variations of suction are responsible for the evolution of LWCS mechanical behaviour. Moreover, strength and stiffness of the treated samples are related to the suction level induced by environmental conditions. The degradation of mechanical behaviour is linked to the number of cycles and to the amplitude of suction variation induced, being the latter responsible for mechanical cement bonding destructuration.

Insights into relationship between mechanical behavior and microstructure evolution of Sn-1.0Ag-0.5Cu-GNSs/Cu joint during thermal cycling

Insights into relationship between mechanical behavior and microstructure evolution of Sn-1.0Ag-0.5Cu-GNSs/Cu joint during thermal cycling

Influence of Microstructure on Dynamic Mechanical Behavior and Damage Evolution of Frozen–Thawed Sandstone Using Computed Tomography

Frost-induced microstructure degradation of rocks is one of the main reasons for the changes in their dynamic mechanical behavior in cold environments. To this end, computed tomography (CT) was performed to quantify the changes in the microstructure of yellow sandstone after freeze-thaw (F-T) action. On this basis, the influence of the microscopic parameters on the dynamic mechanical behavior was studied. The results showed that the strain rate enhanced the dynamic mechanical properties, but the F-T-induced decrease in strength and elastic modulus increased with increasing strain rate. After 40 F-T cycles, the dynamic strength of the samples increased by 41% to 75.6 MPa when the strain rate was increased from 75 to 115 s-1, which is 2.5 times the static strength. Moreover, the dynamic strength and elastic modulus of the sample were linearly and negatively correlated with the fractal dimension and porosity, with the largest decrease rate at 115 s-1, indicating that the microscopic parameters have a crucial influence on dynamic mechanical behavior. When the fractal dimension was increased from 2.56 to 2.67, the dynamic peak strength of the samples under the three impact loads decreased by 43.7 MPa (75 s), 61.8 MPa (95 s), and 71.4 MPa (115 s), respectively. In addition, a damage evolution model under F-T and impact loading was developed considering porosity variation. It was found that the damage development in the sample was highly related to the strain rate and F-T damage. As the strain rate increases, the strain required for damage development gradually decreases with a lower increase rate. In contrast, the strain required for damage development in the sample increases with increasing F-T damage. The research results can be a reference for constructing and maintaining rock structures in cold regions.