Cyclic Impact Loading Research Articles

Mechanical Behavior of Frozen Soil Subjected to Freeze–Thaw Cycle Under Cyclic Impact Load and Passive Confining Pressure

In this study, the effects of freeze–thaw cycles and cyclic impacts on frozen soil were systematically investigated. With an increase in the number of freeze–thaw cycles, the peak stress of frozen soil decreased until a stable state was achieved. Moreover, subjecting frozen soil to an increased number of cyclic impacts led to notable alterations in mechanical characteristics, including peak stress, critical strain and dynamic elasticity modulus. Both the freeze–thaw cycles and cyclic impacts were identified as primary damage mechanisms in understanding frozen soil degradation processes. Damage resulting from these impacts conformed to the Weibull distribution pattern. Damages induced by freeze–thaw cycles, individual impacts and cyclic impacts were integrated into the Zhu–Wang–Tang viscoelastic model (ZWT model). Relying on principles of elastic mechanics, the role of confining pressure on frozen soil was examined and subsequently integrated into an improved ZWT model. To evaluate the model’s effectiveness, its predictions were compared with experimental results.

Integration of carbon nanotube yarns into glass‐fiber reinforced composites for electrical self‐sensing of damage under cyclic bending and impact loading

Integration of carbon nanotube yarns into glass‐fiber reinforced composites for electrical self‐sensing of damage under cyclic bending and impact loading

Evolution of Pore Structure and Fractal Characteristics in Red Sandstone under Cyclic Impact Loading

Fatigue damage can occur in surface rock engineering due to various factors, including earthquakes, blasting, and impacts. The underlying cause for the variations in physical and mechanical properties of the rock resulting from impact loading is the alteration in the internal pore structure. To investigate the evolution characteristics of the pore structure under impact fatigue damage, red sandstone subjected to cyclic impact compression by split Hopkinson pressure bar (SHPB) was analyzed using nuclear magnetic resonance (NMR) technology. The parameters describing the evolution of pore structure were obtained and quantified using fractal methods. The development of the pore structure in rocks subjected to cyclic impact was quantitatively analyzed, and two fractal evolution models based on pore size and pore connectivity were constructed. The results indicate that with an increasing number of impact loading cycles, the porosity of the red sandstone gradually increases, the T2 cutoff (T2c) value decreases, the most probable gray value of magnetic resonance imaging (MRI) increases, the pores’ connectivity is enhanced, and the fractal dimension decreases gradually. Moreover, the pore distribution space tends to transition from three-dimensional to two-dimensional, suggesting the expansion of dominant pores into clusters, forming microfractures or even macroscopic fissures. The findings provide valuable insights into the impact fatigue characteristics of rocks from a microscopic perspective and contribute to the evaluation of time-varying stability and the assessment of progressive damage in rock engineering.

Analysis of the destruction of a die insert used in the industrial process of hot die forging to produce a yoke forging

The article performs an analysis of the destruction of forging dies (with two impressions for a double system) used in the industrial process of forging on a hydraulic hammer to produce a yoke forging with a complex geometry. A detailed analysis was performer on one of the lower dies made of non-standard hot chromium-molybdenum-vanadium tool steel, selected for the tests due to its premature damage (a crack) and relatively low durability equalling only 1200 forgings, that is 600 forged elements. Based on the performed complex studies (surface scanning, microhardness tests, microscopic tests, numerical modelling, impact strength trials) it was demonstrated that the most dangerous destruction mechanism for the analyzed process is mechanical cracking and thermo-mechanical fatigue. As a result of the tool working under extreme conditions (high cyclic mechanical impact loads as well as thermal loads), the most intensive damage of the roughing pass, caused by thermal fatigue and abrasive wear, takes place in the areas of complex geometry as well as intensive flow of the forging material on the radii of the roundings. In turn, in the case of the finishing pass, we observe mechanical fatigue cracking of the tool in the areas of stress and high pressure concentration. The results of FEM modelling combined with the results of a microstructural analysis made it possible to determine the causes of the formation of cracks in the working area of the die, which included cyclic high thermal and mechanical loads as well as abrasive wear as a result of intensive flow of the forging material. Within the conducted studies, directions of further investigations were also proposed in order to improve the durability of the examined tool. Additionally, the observed high tendency of the tool material to crack, based on thermal expansion and impact tests and the determination of the crack resistance coefficient K1C, led to the proposal of an alternative material with higher impact strength.

Dynamic response and deformation failure microscopic characteristics of cyclic impact-cemented tailing backfill.

Frequent blasting disruptions can lead to cumulative damage within the cemented tailing backfill (CTB), increasing the risks associated with mining operations and reducing the recovery rate of the pillar. To address this issue, the Split Hopkinson Pressure Bar (SHPB) was utilized to conduct cyclic impact tests on CTB containing various cement tailing ratios (CTR) at different curing ages. The tests analyzed the stress-strain curve law, dynamic compressive strength (DCS), dynamic strength increase factor (DIF), absorption energy, and deformation failure characteristics of CTB under different impact velocities. Additionally, nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) were employed to investigate the internal pore structural properties of CTB. The research findings indicate that (1) Average strain rate exhibits a linear relationship with the DCS and impact velocity. A lower number of impacts occurred at higher impact velocities and shorter curing age. The number of impacts was drastically reduced when the impact velocity surpassed 3m/s. As the CTR increased, the number of impacts also increased. When the number of impacts increased, the elastic modulus, dynamic impact strength, and peak strain initially increased before ultimately decreasing. (2) Under the cyclic impact load, the shear failure and axial splitting failure were the main failure modes of CTB. Increasing the CTR may be a more effective strategy for reducing the degree of CTB fragmentation compared to prolonging the curing age. When the impact velocity is lower than 3m/s, CTB can withstand multiple impacts and maintain high levels of integrity. When the DIF of the first shock is below 1.5, the CTB demonstrates a capability to withstand more than four shocks. If the DIF exceeds 2, the CTB can only endure a single shock. (3) NMR and SEM observations revealed that CTB itself contains more pores. A dense network structure will grow inside CTB as the curing age and CTR are increased, reducing the porosity. The pore size observed in the samples also support that increasing CTR may be a more effective strategy. Our findings contribute to a better understanding of the kinetic response of CTB in deep mines under frequent blasting disruption and offer a valuable reference point for future research in this area.

The macroscopic and microscopic fatigue failure mechanisms of high-temperature thermally-damaged granite under cyclic impact loading

The rock surrounding wells for developing geothermal energy are in an extreme environment with high temperature and long-term dynamic disturbance. To study the influences of different temperatures and dynamic disturbances on the damage, mechanical properties, and fatigue failure mechanism of rocks, a series of microscopic thermal damage analysis and dynamic cyclic impact tests were conducted on granite specimens treated at 25 ∼ 900 °C. Results show that after being thermally treated to different extents, granite specimens are weakened in terms of the dynamic strength and deformation resistance under cyclic impact loading. As the temperature rises, the number of impacts bearable by specimens before failure decreases accordingly. Under the joint action of temperature and strain rate, 450 °C is found to be the threshold temperature for the significant reduction of dynamic strength of the rock. Under action of temperature and strain rate, the proportion of dissipated energy gradually reduces with rising temperature. Moreover, the dynamic failure mode of rock specimens at high temperatures gradually changes from splitting failure to crushing failure, the fractal dimension gradually increases, and the cumulative dissipated energy density decreases. Finally, the deterioration degree of elastic modulus was adopted to describe the progressive damage evolution of thermally-treated granite under cyclic impact loading. Furthermore, the fracture morphologies of rock specimens after failure were analyzed from the microscopic perspective to reveal the macroscopic and microscopic fatigue failure mechanisms of the rock under the coupling of temperature and strain rate.

Ballast Settlement Accumulation in Zones with Unsupported Sleepers

The high influence of impact and vibration on the behavior of crushed stone and ballast materials has been known for a long time. The zones with unsupported sleepers, which are always present in transition zones, crossings, welds, etc., are typically characterized by impact interaction, ballast full unloading, and additional preloading. However, no studies on ballast layer settlements consider impact vibration loading. Moreover, the influence of the cyclic loading on the ballast settlement intensity is considered ambiguously, with both decelerating and accelerating trends. The comprehensive literature review presents the influence of factors on settlement intensity. The present study aims to estimate the long-term processes of sleeper settlement accumulation depending on the loading factors: impact, cyclic loading, and preloading. The typical for a void zone ballast loading pattern was determined for various void sizes and the position along the track by using a model of vehicle-track interaction that was validated by experimental measurements. The loading patterns were parametrized with four parameters: maxima of the cyclic loading, impact loading, sleeper acceleration, and minimal preloading. A specially prepared DEM simulation model was used to estimate the ballast settlement intensity after initial settlement stabilization for more than 100 loading patterns of the void zone cases. The settlement simulation results clearly show that even a low-impact loading pattern causes many times increased settlement intensity than ordinary cyclic loading. Moreover, the initial preloading in the neighbor-to-void zones can cause even a decrease in the settlement intensity compared to the full ordinary or partial unloading. A statistical analysis using a machine learning approach and an analytic one was used to create the model for the intensity prediction regarding the loading patterns. The analytic approach demonstrates somewhat lower prediction quality, but it allows to receive plausible and simple analytic equations of the settlement intensity. The results show that the maximal cyclic loading has a nonlinear influence on the settlement intensity that corresponds to the 3–4 power function, and the impact loading is expressed by the linear to parabolic function. The ballast’s minimal preloading contributes to the reduction of the settlement intensity, especially for high cyclic loadings that are typical for neighbor-to-void zones. The results of the present study could be used for the complementing of the present phenomenological equations with the new factors and further application in the algorithms of the settlements accumulation prediction.

Advances in Shear-Seepage Properties of Rock Mass Filled with Joint Fissure

Since joint fissures are distributed extensively within rock masses, rock masses evolve into "sandwich" shapes when filled with joint fissures under long-term geological action, which causes rock discontinuities and destroys rock stability. This study reviews the advances in the shear-seepage properties of rock masses filled with joint fissures (RMFJFs) under static, quasistatic, and dynamic loads, including laboratory experiments, theoretical analysis, and numerical calculations. Results show that the shear properties of RMFJFs are closely associated with the strength of the fillings, the filling degree, and the roughness of the joints. RMFJFs develop under the stress of surrounding rocks, and their seepage properties are therefore affected by the surrounding stress and the filling degree, the rock layer thickness, and the porosity of the rock or fillings. However, detailed studies on the seepage properties of RMFJFs under cyclic loading, impact loading, and different shear rates are lacking. Finally, the existing problems in the research on the seepage properties of RMFJFs are clarified, a constructive research strategy is proposed, and the related trends are discussed in light of the overall mechanical behavior of RMFJFs.

Progressive damage and fracture behavior of brittle rock under multi-axial prestress constraint and cyclic impact load coupling

To explore the progressive damage and fracture mechanics characteristics of brittle rock materials under combined dynamic-static loading. Taking account of the coupling effect of the constraint states of uniaxial stress (σ1 ≥ σ2 = σ3 = 0), biaxial stress (σ1 ≥ σ2 > σ3 = 0) and true triaxial stress (σ1 ≥ σ2 ≥ σ3 ≠ 0) and impact load, the strain rate effect and prestress constraint effect of dynamic mechanical characteristics of sandstone are studied. The progressive damage evolution law of sandstone under the coupling of true triaxial stress constraint and cyclic impact load is discussed. The results show that with the increase of axial stress σ1, the dynamic compressive strength and peak strain gradually decrease, and the strain rate gradually increases, resulting in crushing failure under high strain rate. When the axial stress is fixed, the lateral stress constraint reduces the damage degree of sandstone and improves the dynamic compressive strength. With the increase of strain rate, the sample changes from slight splitting failure to inclined shear failure mode. Under the true triaxial stress constraint, the intermediate principal stress σ2 obviously enhances the dynamic compressive strength of sandstone. Under the constraints of triaxial stress, biaxial stress and uniaxial stress, the enhancement effect of dynamic compressive strength and the deformation resistance of sandstone are weakened in turn. Under the coupling of true triaxial stress constraint and high strain rate, sandstone samples show obvious progressive damage evolution effect under repeated impacts, and eventually inclined shear failure occurs, resulting in complete loss of bearing capacity.

Damage deterioration mechanism and damage constitutive modelling of marble after cyclic impact loading

Rock mass in tunnel, underground chamber and other underground engineering is inevitably affected by multiple blasting impact, rock mass cracking and failure are often affected by these damaged rock mass, so it is meaningful to study the rock mass affected by dynamic damage. To explore the influence of cyclic impact on the internal structure of marble, NMR (Nuclear Magnetic Resonance) technique was adopted to test the marble. It was found that the impact would rise the porosity of marble, and the pore size distribution would also change greatly. Then uniaxial compression experiments were conducted on core samples. The results show that the impact will cause significant damage to the marble, and the mechanical properties of the marble will be obviously degraded. With the increase of impact times, the peak strength and tangential deformation modulus tend to decrease. The impact effect promotes the initiation and development of rock microcracks, pushes forward the development of the compaction stage, and increases the strain at the full compaction point. In addition, the damage constitutive model with the combination of different disturbances and loads was constructed in stages according to the principle of statistics, and the experimental results were used to verify the damage constitutive model. The crack closure and failure of the samples subjected to different impact times were well reflected in the model, and the practical significance of the parameters in the model was analyzed. The failure mode of the sample subjected to different impact times is discussed and verified by acoustic emission technology.

Energy Dissipation and Fractal Properties of Coal under Cyclic Impact Loading

To investigate the periodic disturbance and damage characteristics of coal under different impact pressures, the stress‒strain failure and damage trends of weak, impact‐prone coal samples were analysed under different impact pressures and different numbers of impacts. Split‐Hopkinson pressure bar (SHPB) tests were conducted to study the stress‒strain curve, dynamic compressive strength, elastic modulus, failure strain, and absorbed energy responses with different numbers of impacts and different strain rates. Fractal theory and methods were applied to analyse the influence of different impact pressures and different numbers of impacts on coal sample failure to reveal the relationship between the number of impacts and the fractal size characteristics of coal fragmentation. The energy modes and failure modes of coal samples under different impact effects were analysed under dynamic loading. Regarding the energy absorption corresponding to different numbers of impacts, the energy absorption per unit volume (EAPUV) of three impacts was calculated to be 0.46 J/cm3. The number of impacts was directly correlated with the energy absorbed by the coal sample. Furthermore, the number of impacts was directly correlated with the severity of the deformation and damage of the coal sample and was inversely correlated with the fragmentation of the coal sample. The degree of coal sample fragmentation was directly proportional to the number of impacts, and the fractal dimension increased with the number of impacts. The study of the failure and fractal characteristics of coal samples under different impact pressures and different numbers of impacts provides important information for the prevention and control of coal mine rock bursts.

Research on the Energy Dissipation Patterns and Fragment Size Distribution Characteristics of Coal Under Cyclic Impact Loading With Confining Pressure

Research on the Energy Dissipation Patterns and Fragment Size Distribution Characteristics of Coal Under Cyclic Impact Loading With Confining Pressure

Study on dynamic characteristics of red sandstone under cyclic impact

In order to study the dynamic characteristics of red sandstone under cyclic impact, the cyclic impact test of red sandstone at the same incident velocity was carried out by E-SHPB test device. Through the analysis and summary of the test data, the influence of cyclic loading times on the dynamic compressive strength of red sandstone and the failure process of red sandstone under the impact of 1000v loading voltage are discussed. The test results show that under the impact of 1000v loading voltage, the peak stress of the specimen decreases linearly with the increase of the number of impacts. The dynamic compressive strength of the specimen under the fifth cyclic impact loading is about 9MPa lower than that under the first impact, and the resistance to deformation is weakened. With the increase of the number of impacts, the cracks in the specimen are continuously generated and expanded, and the specimen is mainly split failure.

Cyclic Impact Test with the Hopkinson Bar: Application to Granite

A laboratory scale cyclic impact loading test was developed by modifying a Hopkinson Bar test setup. The modifications involve placing a special shank piece between the striker and the rest of the setup. The shank transmits the impact loading and enables the use of compressed air for rapid reloading of the striker. The short shank is in direct contact with the specimen, i.e., there is no long input bar. With this configuration residual wave motion and reloading of the specimen is avoided. Behind the striker an output bar and momentum trap bar are placed for specimen loading measurement and removal of the wave motion in the system, respectively. The trap bar is stopped by a pneumatic actuator, which also resets the bars and the specimen before the next impact loading. The compressed air flow driving the striker is controlled by high-speed electropneumatic valves connected to a control unit and operated in simple open-loop control. Numerical simulations of both the striker motion by compressed air and dynamic loading wave propagation during impact were used in the design phase as well as setting up the test parameters. The test setup is able to produce stable cyclic impact loading at a frequency of up to 10 impacts per second with striker velocity up to 9 m/s. The feasibility of the test method is demonstrated by providing data from cyclic Brazilian disc experiments on Balmoral Red granite at both impact and quasi-static cyclic loading.

Influence of cyclic dynamic disturbance on damage evolution and zoning effect of coal-rock under local static load constraint

In order to obtain the characteristics of the effects of cyclic impact loading on the damage of coal-rock in the presence of a local static load constraint, the evolution of the damage factor and the fracture rate during the process and incremental cyclic impact on raw coal and briquettes has been studied. Experimental results show that the presence of local static load restraint improves the impact resistance of the coal-rock, and the damage factor of the coal-rock shows obvious zoning characteristics. When the coal-rock is in an elastic state, the partition with a larger static load restraint area has stronger impact resistance, when the coal-rock is in a plastic state, the partition with a larger static load restraint area has a weaker impact resistance. Increasing impulsive cyclic impacts have a higher damage efficiency to coal-rock than constant impulsive cyclic impacts. The difference in rock breaking efficiency between the two cyclic impact methods is mainly reflected in the partition with the largest constrained area. The crack propagation on the coal-rock surface is more consistent with the partition characteristics of the damage factor. When the static load constrained zone is in an elastic state, the static load has an inhibitory effect on the crack growth. When the static load confinement zone is in a plastic state, the cracks mainly propagate in the static load confinement zone, and the constrained zone mainly consists of tensile cracks that grow in the vertical direction, while the cracks in the non-constrained zone mainly grow in an oblique direction. Finally, fracture mechanics was applied to analyze the failure type of the sample.

Effect of nitrogen on the structure and properties of Zr-Si-B-N coatings deposited by magnetron sputtering

Protective Zr-Si-B-N coatings were deposited by magnetron sputtering of the 66%ZrB2 + 26%ZrSi2 + 6%Si + 2%ZrO2 composite target at varied partial pressure of nitrogen. The coatings were studied in terms of structure, optical characteristics, mechanical and tribological properties, cyclic impact and oxidation resistance. All the coatings were characterized by a dense and defect-free structure, without any well-defined columnar elements. The base of the non-reactive Zr-Si-B coatings was the hexagonal ZrB2 phase with the crystallite size of about 20 nm. Nitrogen doping led to grain size reduction and coating amorphization. An increase in the nitrogen concentration leads to the formation of an amorphous phase а-Si(Zr)BN. The high content of nonmetallic bonds ensured the high transmittance (up to 90 %) in the visible and infrared spectral ranges for the coatings characterized by the maximum nitrogen content. Hardness of the coatings deposited in working gas Ar and Ar + 15%N2 was ~20 GPa. When the coatings were deposited in an atmosphere of pure nitrogen, this value was ≤15 GPa. Due to structure modification as well as increasing elastic recovery and elastic strain to failure, nitrogen doping of the coatings contributed to reduction of the friction coefficient and increased wear resistance under sliding friction conditions and cyclic impact loading. High-temperature oxidation resistance and thermal stability of the coatings decreased after nitrogen doping. The Zr-Si-B coating exhibited the highest oxidation resistance and withstood long-term exposure to 1200 °C and short-term exposure to 1400 °C. The high protective properties were ensured by formation of the silica-based surface protective layer with zirconia crystallites dispersed in it.

Failure characteristics and service life prediction of polycrystalline diamond compact (PDC) cutter under cyclic impact loading

This paper aims to investigate the cyclic impact damage characteristics and service life of PDC cutters under varying impact loadings, angles, and depths. Additionally, a life prediction model is established to predict the fatigue life of flat cutters, axe cutters, and triangular cutters. A customized impact test device was utilized to conduct the cyclic impact test, and a finite element model was calibrated based on the experiment result of flat PDC cutter. Then, the model was used to analyze the stress distribution in the axe and triangular cutters, respectively. By combining the experimental and numerical results, the S–N (Stress-Number of times) curve representing the fatigue failure of the PDC cutter substrate was established. Moreover, the fatigue life of different PDC cutters under impact loading was predicted by integrating the S–N curve with the results of finite element stress analysis. The findings indicate that triangular cutters exhibited the longest fatigue life, with a 30.36% increase compared to flat cutters, under an impact angle of 15°, an impact depth of 4 mm, and an impact loading of 7616N. Similarly, the fatigue life of axe cutters was 7.59% higher than that of flat cutters. These findings suggest that non-flat cutters have greater impact resistance and are more suitable for heterogeneous strata characterized by significant impact stress variations.

Dynamic Behaviour and Energy Evolution of Granite in a Tunnel Under Cyclic Impact Loading

Dynamic Behaviour and Energy Evolution of Granite in a Tunnel Under Cyclic Impact Loading

Effect of CrAIN coating properties on impact fatigue of tool steel

The tools in forming processes are subjected to cyclic impact loads. Physical vapor deposition (PVD) coatings can potentially improve the service life of such tools, given the effect of coating properties on impact fatigue of coated substrate is well-understood. Previous investigations on the cyclic impact loading of PVD coated tool steels mainly correlate the plastic deformation of the substrate to the resulting coating cracks. Hereby, the effect of underlying elastic-plastic coating deformation mechanism in combination with coating properties needs further clarification. Therefore, the current work aims to investigate the combined effect of thickness, morphology, elastic-plastic deformation and residual stress state of the coating on the impact fatigue behavior of coated tool steel substrates. For this purpose, (Cr90Al10)N and (Cr66Al34)N coatings, each with a thickness of s = ∼ 1.7 μm and s = ∼3.5 μm, were deposited on HS6–5-2C substrates. In addition to coating characterization, the residual stresses were measured by focused ion beam-digital image correlation (FIB-DIC) ring-core method. The elastic-plastic deformation of the coatings was studied by nanoindentation. The coated samples were subjected to cyclic impact loading with an initial hertzian contact pressure pH = ∼ 9.7 GPa and frequency f = 50 Hz for N = 0.1, 0.5 and 1 million impacts. The impact imprints were analyzed using high resolution electron microscopy to study the coating deformation mechanism in combination with fatigue cracks initiation. Columnar inclination and shear gliding along the column boundaries resulted in the initiation of fatigue cracks in the coating around the boundary region of impact imprint. The chemical composition, morphology, residual stress state and elastic-plastic deformation behavior of the coating cumulatively affected the impact fatigue as thick coatings showed reduced resistance against initiation of fatigue cracks. The investigation contributes to adjusting the PVD coating thickness and resulting coating properties for higher tool service life in applications involving cyclic impact loading.

Effects of low cycle impact fatigue on the residual mode II fracture energy of adhesively bonded joints

Cyclic loading exerts a profound influence on the durability of adhesively bonded joints, particularly under cyclic impact loads. Under normal cyclic loading, adhesive joints typically reach their fatigue limit when subjected to approximately 50% of their maximum static strength. However, the endurance limit is considerably lower for cyclic impact loading, sometimes even falling below 5% of the impact strength. This paper investigates the effects of low-energy cyclic impacts on the fracture energy of an end-notched flexure (ENF) joint bonded with an epoxy-based adhesive. The study includes an analysis of the static fracture energy of the ENF joints prior to subjecting them to repeated impact cycles. Additionally, certain joints were subjected to repeated impact cycles until complete crack propagation occurred. To evaluate the residual critical fracture energy of these joints, certain cyclic impact tests were interrupted, and the joints were subsequently subjected to quasi-static loading conditions. The results reveal the remarkable sensitivity of the fracture energy of adhesive joints to the impact energy level, challenging the assumption of infinite life under cyclic impacts often made in conventional fatigue tests. Stress concentration caused by cyclic impact stress waves leads to a higher density of cracks at the specimen edges. The findings are supported by numerical analysis conducted in this study. These results underscore the importance of comprehensive inspections for bonded structures exposed to low-energy cyclic impacts, as impact fatigue can significantly diminish joint strength. The fracture energy decreases as the number of impact cycles increases, indicating a cumulative effect. The findings contribute to a better understanding of the mode II fracture behavior of adhesively bonded joints under repeated impact loads and provide insights for safe design and inspection practices.