Damage Law Research Articles

Study on the Impact Resistance of the Honeycomb Composite Sandwich Structure by a Fragment Flight Angle

At present, the typical targets in the air are mainly high-speed impact bodies such as fragments, which pose a great threat to aviation equipment such as drones. It is urgent to study the impact resistance of different initial conditions of fragments to honeycomb sandwich structures. The fragment impact experiment analyzes the fragment flight attitude, fragment power, failure mode, and impact resistance of the structure by changing the different impact velocities on the target plate. In order to study the damage mode and anti-damage performance of several composite honeycomb sandwich structures under oblique penetration impact mode, a total of six groups of composite honeycomb structures were tested by fragment impact sandwich structure at different angles, and the damage law of composite honeycomb sandwich structure in the experiment was compared and analyzed. According to the experimental results, the accuracy of the theoretical model and numerical simulation was verified by fragment impact composite honeycomb sandwich structure. The analysis results show that the failure mode of the composite honeycomb sandwich structure under oblique impact is quite different from that of the traditional structure, which is mainly reflected in the material accumulation type of the failure part. Compared with the traditional structure, the composite honeycomb sandwich structure exhibits better energy absorption efficiency, which is increased by 130% and 600%, respectively. This paper shows the different failure modes of honeycomb sandwich structure under oblique impact and positive impact. The existence of an inclined angle changes the failure mode, increases the damage range, and increases the total energy absorption. It is necessary to further study the failure mechanism of fragment flight angle on honeycomb sandwich structure and provide a reference for the impact resistance design of the structure.

Study on progressive damage and deformation law of coal body around borehole under different moisture states

Study on progressive damage and deformation law of coal body around borehole under different moisture states

Validity of Laws for Predicting Lifespan of Welded Points Under Variable Loading

The article examines the validity of the laws for predicting the life of welded points under variable amplitude loading, using three steels (HE360D, XE360D and XES) supplied by ArcelorMittal to Renault for the manufacture of automobile chassis parts. The fatigue tests revealed two modes of failure: cracking of the sheets at medium stresses and shearing of the molten core at high forces. For lifespan prediction, three damage laws were studied: Miner's law, Mesmacque and Amrouche law, and a proposed model. Miner's law, despite its simplicity and wide distribution, shows notable limitations in the presence of variable loads, because it does not take into account the interactions between successive load levels. The law of Mesmacque and Amrouche uses a damage indicator linked to the FN curve of the material, allowing a cycle by cycle estimation of the residual lifespan. However, it remains non-conservative at low effort. The proposed model, based on Chaboche law, overcomes some of its theoretical drawbacks, notably the dependence on the calibration parameters of the SN curve. By fitting this curve within a specific calibration window, the model improves forecast accuracy by taking into account parameter variability. This proposed model provides more reliable lifespan predictions that better correlate with experimental results, especially for low effort levels where Miner's law fails. The validation approach is based on comparing the predictions of the damage laws with the experimental results, by evaluating the deviation from the first bisector of the graphs. The results show that Miner's law is unsuitable for effort levels, while the proposed model turns out to be the most precise and conservative. The law of Mesmacque and Amrouche falls between the two, presenting a certain justice but remaining overall non-conservative. In conclusion, the proposed model offers a better match with experimental data, making its predictions more reliable for industrial applications.

Analysis of shear creep damage model of slope rock mass under the influence of coupled damage effects (DBSM)

Abstract This article reveals the evolution law of shear creep damage of carbonaceous shale (weak interlayer of slope) under dynamic load from a mechanical perspective by combining indoor experiments and theoretical research. Firstly, a coupled damage variable D BSM was established for the initial damage D 0 and dynamic disturbance shear creep damage D BS of rock mass based on the theory of damage mechanics. Secondly, according to the fractional calculus operator theory and considering the influence of coupled damage variable D BSM on the viscosity coefficient of rock mass in the viscoelasticity and viscoplasticity creep stages, a shear creep damage model of rock mass was established. At the same time, combined with the shear creep test data under the influence of dynamic loads, the damage evolution law of shear creep in carbonaceous shale (weak interlayer of slope) was revealed, and the accuracy of the established shear creep damage model was verified. Finally, the damage evolution law of carbonaceous shale was quantitatively analyzed. Results show that: The shear creep damage model established in this article has unique advantages. The greater the initial damage, the more likely shear creep failure is to occur under the influence of dynamic disturbance and shear creep loads. Dynamic disturbance accelerates the damage of weak interlayers of slope. The cumulative coupling damage of carbonaceous shale (D ma ≤0.18) under dynamic disturbance and multi-stage shear creep loads exhibits an S-like evolution pattern. The shear creep damage mechanism of carbonaceous shale is characterized by obvious initial damage effect, dynamic disturbance damage effect, and stress response characteristics.

Modeling method of random collision of ellipsoidal particles in mechanical simulation for high energy solid propellant

Abstract It is based on the molecular dynamics algorithm of elliptical optimization to establish a mesostructure model of oval particles of high-energy solid propellant considering gradation and controllable filling rate according to the mesostructure characteristics of high-energy solid propellant. The bilinear cohesion model was applied to describe the interface damage behavior and carry out the high-energy propellant tensile test at three rates. The rationality of the elliptical particle model has been verified between the comparison of the calculated results with the experimental results established to describe the micromechanical behavior of high-energy propellants, which is to reveal the mesoscopic damage law of high-energy solid propellant under different tensile rates in this paper.

Creep damage laws for bonded joints under pure mode II loading

Adhesively bonded joints have played an important role in several industries, mainly in automotive and aeronautics. A wide range of studies have been presented on the evaluation of the static behaviour of bonded joints, considering pure modes I and II, but also mixed-mode I + II loading. More recently, some developments have been done on the analysis of fatigue loading in this type of structural elements, introducing the importance of studying damage cohesively, along a determined period of time. As fatigue loading, creep loading can provide a significant contribution in terms of damage during the lifetime of a given bonded joint. Few studies were presented in the literature, regarding creep loading in bonded joints, so that a cohesive model capable of predicting the corresponding mechanical behaviour is needed. Twelve damage laws were postulated in this study, being used in a new cohesive zone model, predicting the creep behaviour of bonded joints under pure mode II loading. The corresponding implementation was proved, after an in-depth parametric analysis. The presented study constitutes a basis for future developments on the cohesive damage modelling of bonded joints, considering mixed-mode I + II loading scenarios.

Dynamic Response and Damage Analysis of a Large Steel Tank Impacted by an Explosive Fragment

Abstract The fragments generated by explosions of storage tanks in chemical industrial parks may cause perforations or dents in adjacent tanks and trigger a domino effect. This paper determined reasonable fragment parameters based on the statistical laws of accidents and empirical formulas. The dynamic response process of large steel tanks impacted by fragments was simulated with ls-dyna. The typical impact process and results were analyzed in detail, and the damage laws of the tanks were discussed under various filling coefficients, volumes, fragment velocities, and impact angles. The results indicate that the inertial resistance of the inner liquid shortens the impact duration. Multiple collisions occur between the fragment and tank during impact, and the impact process involves three stages: initial collision, crushing and collision, and separation flight. The impact center displacement shows a fast and then slow reduction trend as the liquid level height increases, and the damage to the tank is negatively correlated with the liquid level height. The damage is lower when the tank volume is larger in an empty tank or at a high liquid level, while the damage instead increases when the volume exceeds 5000 m3 at a low liquid level. The peak impact force of the end-cap fragment is greatest when frontal impact occurs. Fragment flipping and curling occur at 45 deg and 90 deg impact, respectively. As the vertical impact angle increases from 0 deg to 90 deg, the fragment impact mode changes from initial frontal impact to flip detachment and finally to curling deformation.

Cellular Automata-Based Experimental Study on the Evolution of Corrosion Damage in Bridge Cable Steel Wire

Cable-stayed bridges have become the preferred bridge type for large-span bridges due to their unique advantages, and the long-term performance of the cable under the extreme conditions has been facing great challenges. An accelerated corrosion test was carried out using in-service cable, and the evolution model of the etch pit was established based on cellular automata to study the evolution law of corrosion damage to steel wire. This study showed that with the increase in the number of dry-wet cycles in the electrified accelerated corrosion, the macro- and micromorphology of the steel wire showed more serious corrosion damage, the tensile strength decreased, the ductility index decreased, and the tensile strength of the steel wire after corrosion decreased by nearly 5%; the geometric dimension of the steel wire etch pits all met a right-skewed distribution with a broader range of etch pit depth, mainly consisting of shallow spherical etch pits and deep ellipsoidal etch pits. The length, width, and depth sizes were mainly distributed in the range of 0.005 mm to 0.015 mm, 0.005 mm to 0.02 mm, and 0 mm to 0.04 mm; at the early stage of corrosion, the etch pits were first developed along the longitudinal direction. As the corrosion process progressed, the iron matrix participated in the electrochemical reaction, leading to the rapid expansion of the etch pits’ dimensions. The stress concentration effect at the bottom of the etch pit caused the maximum stress to approach 1800 MPa, with a stress concentration coefficient of more than 3.0; when the cable anchorage system was located in the connecting sleeve and the threaded splice seam, where corrosion protection was prone to failure, the outer steel wire bore most of the corrosive effects, and the internal cable was less eroded by the corrosive medium.

Study on mechanical properties and anti-erosion performance of fiber reinforced seawater sea sand concrete

In order to study the mechanical properties of seawater sea sand concrete and the durability damage law of seawater sea sand concrete under the action of seawater erosion, corresponding specimens were prepared and subjected to cube compressive strength, flexural strength, and dry-wet cycle tests by taking the volume dosage of glass fibers and polyvinyl alcohol fibers as variables. The test combined SEM scanning and EDS to analyze the microstructure of fiber-reinforced seawater sand concrete, and established a model based on the two-parameter Weibull probability distribution. The results show that the fiber has a significant effect on improving the mechanical properties and erosion resistance of seawater sand concrete. When the total volume content is 0.3% and the mixing ratio is 1:1, the improvement effect is the best. The maximum increase in cubic compressive strength was 24.2%; the maximum increase in flexural strength was 38.8%. After the specimens were subjected to wet and dry cycles for 360d, the maximum reduction in mass loss rate was 41.23%; the maximum reduction in strength loss rate was 27.55%. As observed from the microscopic images, the main disadvantage of SSC is that the salt crystallization and swelling matter produced by the erosion ions will weaken the bond between aggregate and mortar, resulting in defects in the interfacial transition zone (ITZ). Under the action of dry-wet cycles, the alternating dry-wet forces, the expansion pressure generated by expansive substances and the crystallization pressure generated by salt crystallization will change the microstructure, and therefore the damage of the specimen will deepen with the extension of erosion time. The microscopic images also show that the doping fibers can improve the internal integrity and compactness of the matrix, thus significantly improving the mechanical properties and durability of seawater sea sand concrete. In this test, a damage model was established based on the two-parameter Weibull distribution model, and the damage law between strength loss and dry-wet cycles was fitted, which provides a favorable basis to study the damage of seawater sea sand concrete under wet-dry cycling.

Evolution and Characterization of Uniaxial Compression Damage of Coal Measure Rock

In order to study the evolution law of uniaxial compression damage and its characterization method, three kinds of rocks with different lithology that commonly exist in coal measure rock were taken as the research objects to explore the relationship between their mineral composition, microstructure and mechanical properties, and the feasibility of acoustic emission (AE) characteristic parameters and AE spatial location to characterize the evolution process of uniaxial compression damage of rocks was compared and analyzed. A damage constitutive model based on AE cumulative ringing count was established and verified by numerical simulation. The results show that the differences in the micromorphology and mineral composition of coal measures with different lithology directly affect their physical and mechanical properties and load damage characteristics. AE characteristic ringing count can effectively represent the damage evolution process of rock during loading. Based on rock porosity characteristics and AE cumulative ringing count during loading, a constitutive model considering initial damage and cumulative damage was established. The theoretical analysis results of the damage constitutive model are in good agreement with the results of laboratory experiments and numerical simulation, which can be used to analyze the damage process of coal measure rock under load.

Lifespan Evaluation for a Standard RV Reducer based on Fatigue Strength Theory

Rotate vector (RV) reducers are the two-stage deceleration device comprising involute and cycloid-pin gear transmission mechanisms. As the typical deceleration elements, they are widely applied in industrial robots, digitally controlled machine tools and automation fields due to their compact structure and high precision. However, a reducer may lose precision after a long-term operation. Moreover, pitting and metal peeling of internal components may also occur, leading to a fatigue failure. Therefore, it is necessary to conduct investigations on lifespan evaluation for RV reducers. In this study, the CRV-80E reducer is taken as the research object. Firstly, according to its transmission characteristics, the lifespan evaluation model for a standard RV reducer is established based on fatigue strength theory and Palmgren-Miner linear cumulative damage law, with the internal crankshaft bearing is considered as the key component. Then, the simulations are carried out on crankshaft bearing by the ANSYS Workbench and SKF SimPro. The contact stress, deformation on bearing rollers, and the rated lifespan of the reducer are simulated. Finally, the accelerated life test is conducted on an RV reducer by increasing the external load with the positioning precision as an output and criterion. After the test, the reducer is disassembled, and metal peeling failure is observed on the crankshaft bearing while other parts are relatively intact. The test results validate the feasibility and accuracy of the service life evaluation model and simulation analysis. This study provides a new research approach for researchers and manufacturers and a design reference for engineers to improve the lifespan of RV reducers by optimizing crankshaft bearings, which have a certain academic value.

Sprain energy consequences for damage localization and fracture mechanics

The 2023 smooth Lagrangian Crack-Band Model (slCBM), inspired by the 2020 invention of the gap test, prevented spurious damage localization during fracture growth by introducing the second gradient of the displacement field vector, named the "sprain," as the localization limiter. The key idea was that, in the finite element implementation, the displacement vector and its gradient should be treated as independent fields with the lowest ([Formula: see text]) continuity, constrained by a second-order Lagrange multiplier tensor. Coupled with a realistic constitutive law for triaxial softening damage, such as microplane model M7, the known limitations of the classical Crack Band Model were eliminated. Here, we show that the slCBM closely reproduces the size effect revealed by the gap test at various crack-parallel stresses. To describe it, we present an approximate corrective formula, although a strong loading-path dependence limits its applicability. Except for the rare case of zero crack-parallel stresses, the fracture predictions of the line crack models (linear elastic fracture mechanics, phase-field, extended finite element method (XFEM), cohesive crack models) can be as much as 100% in error. We argue that the localization limiter concept must be extended by including the resistance to material rotation gradients. We also show that, without this resistance, the existing strain-gradient damage theories may predict a wrong fracture pattern and have, for Mode II and III fractures, a load capacity error as much as 55%. Finally, we argue that the crack-parallel stress effect must occur in all materials, ranging from concrete to atomistically sharp cracks in crystals.

Study of the law of strength attenuation and microstructure damage to cement improved loess under acid rain erosion

Study of the law of strength attenuation and microstructure damage to cement improved loess under acid rain erosion

Normal high velocity solid dust impacts on tiles of tokamak-relevant temperature

Runaway electron incidence on plasma facing components triggers explosive events that are accompanied by the expulsion of fast solid debris. Subsequent dust-wall high speed impacts constitute a mechanism of wall damage and dust destruction. Empirical damage laws that can be employed for erosion estimates are based on room-temperature impact experiments. We use light-gas gun shooting systems to accelerate solid tungsten dust to near-supersonic speeds towards bulk tungsten targets that are maintained at different temperatures. This concerns targets cooled down to −100°C with liquid nitrogen and targets resistively heated up to 400 °C. Post-mortem surface analysis reveals that the three erosion regimes (plastic deformation, bonding, partial disintegration) weakly depend on the target temperature within the investigated range. It is concluded that empirical damage laws based on room-temperature measurements can be safely employed for predictions.

Analysis of dynamic disturbance and multistage shear creep damage evolution law of the weak intercalated layers in slope under the influence of coupled damage effect

Based on the damage characteristics of multistage shear creep in weak intercalated layers (carbonaceous mud shale) of slopes under the influence of dynamic disturbance, the effective bearing area method was used. A new coupled damage equation (dynamic disturbance damage, shear creep damage, and initial damage) was established through further derivation, and its applicability was demonstrated. The calculation method for the relevant coupled damage degrees was also provided. Furthermore, by targeting the three coupled damage factors and extending the Kachanov damage law, a time-dependent damage evolution equation for weak intercalated layers under the influence of the three coupled damage effects was established. The influence of different dynamic disturbance intensities on the evolution of multistage shear creep damage in weak intercalated layers of slopes under the influence of coupled damage effects was analysed. The results show that the damage to the rock mass caused by dynamic disturbance mainly occurs in the low-frequency stage (40–80 Hz). The instantaneous damage caused by dynamic disturbance to the shear plane of weak intercalated layers is not only affected by the intensity of the dynamic disturbance but also limited by the magnitude of the shear creep load. The influence of the dynamic disturbance intensity on the entire process of multistage shear creep damage of weak intercalated layers was analysed. With increasing of dynamic disturbance intensity, the cumulative coupled damage at the end of shear creep at all levels gradually exhibits linear evolution. The time-dependent coupling damage evolution process of weak intercalated layers was quantitatively characterized.

Characteristics of soil moisture transport in the aeration zone of subsidence areas under the disturbance of coal seam mining

High-intensity coal mining has induced a series of ecological and environmental problems issues, including surface subsidence, the development of ground cracks, and the deterioration of vegetation. The disruption of water circulation systems induced by mining, such as perched groundwater, groundwater of aeration zone, and phreatic water, is the root cause of vegetation withering. The aeration zone serves as a crucial nexus in the process of water cycling and exerts a significant influence on soil fertility. To explore the characteristics of soil moisture transport in subsidence areas under the mining disturbance, on-site monitoring of the size and morphology characteristics of subsidence areas and ground cracks was conducted in typical mining areas in Inner Mongolia, China. Subsequently, a typical soil moisture transport model was constructed in subsidence areas, the soil moisture transport patterns under the influence of different types of subsidence and cracks were analyzed, and the influence law of soil damage on soil moisture transport in the aerated zone was clarified. The results indicate that (1) Based on the occurrence and distribution characteristics of subsidence cracks, the subsidence area can be divided into tension zone, compression zone, and neutral zone; the ground cracks are divided into permanent tension cracks and dynamic cracks. (2) The drought stress effect of soil in the subsidence area is significant. Under the influence of soil structure variation, the water-holding capacity of the soil in the subsidence area decreases, and the soil moisture dissipation is strong. The soil moisture transport rate in the aeration zone of the subsidence area is ranked as follows: tension zone > neutral zone > compression zone. (3) Ground cracks can exacerbate the soil moisture transport rate in the aeration zone. After 15 d of crack appearance, the soil moisture transport reaches a relatively stable state, and the soil moisture transport rate in the surface layer of the crack is the fastest, and the loss of soil moisture is the most significant. The crack effect is not significant beyond 100 cm from the crack. This study provides a theoretical and data support for soil and vegetation remediation in mining subsidence areas.

Spatio-temporal evolution law of anisotropic shear damage on rock mass joint surface affected by joint morphology

The spatial–temporal evolution law of shear damage on the joint surface is closely related to its morphological characteristics. Understanding the heterogeneous failure behavior of the joint surface is essential for revealing the controlling role of the joint morphology. The diorite from the Guanshan Tunnel is investigated through anisotropic direct shear tests in this study. Based on shear damage quantification and acoustic emission (AE) localization techniques, the heterogeneous damage evolution law of joint surfaces under different joint compression strength (JCS), normal stress (σn), and morphology parameter (M) is studied. The results indicate that the joint surface morphology, shear damage, and AE parameters exhibit similar anisotropic characteristics in different shear directions. An increase in the morphology parameter leads to an increase in shear failure, with shear fracture energy and the number of fracture events showing an increasing trend. Meanwhile, the occurrence of a large number of fracture points shifts from the pre-peak nonlinear period to the post-peak period. However, the evolution process of fracture events exhibits certain similarities, though the morphology parameters are different in two opposite shear directions. Additionally, shear damage volume and fracture energy demonstrate consistency in spatial distribution and quantitative characteristics, while the linear scale factor between cumulative shear fracture energy and damage volume decreases with increasing joint surface strength. These findings assist in a better understanding of the anti-sliding property of joint surfaces and provide crucial clues for further exploration of joint surface failure mechanisms.

Research on improving the flexural performance of alkali-activated geopolymer cemented coal gangue through layered addition of fibers

The brittle characteristics of geopolymers during failure seriously hinder their practical engineering applications. To improve the toughness of low-energy alkali-activated geopolymer cementing coal gangue (AGCCG), the flexural performance of alkali-activated geopolymer cementing coal gangue (AGCCG) was enhanced by layering polypropylene fibers. Based on DIC digital speckle technology, the four-point flexure test of AGCCG was carried out, and the strength formation mechanism of the material was analyzed in depth by combining SEM-EDS and XRD. 3D visualization and analysis of the inside of the specimen with the help of CT scanning technology. The internal crack evolution law of the sample was illustrated by PFC numerical simulation. The results showed that the crack formation threshold, peak flexural strength and residual flexural strength of the specimens reached a local maximum at 3 % NaOH doping. With the increase of NaOH dosage, the cementitious product becomes more and more dense and homogeneous, and the area of void defects in the hydration product within the field of view becomes smaller and smaller. The peak bending strength of specimen B4-#4 is 79.43 % of that of specimen B5-#1–4, in which the cost of specimen B5-#1–4 is four times of that of specimen B4-#4, and the way of fiber assignment in specimen B4-#4 is more reasonable when considered together. The layered addition of fibers has a directional strengthening effect on the mechanical properties of geopolymer, and the overall addition of fibers can improve the overall strength and toughness of geopolymer. The numerical simulation results basically coincide with the macroscopic test results, and are consistent with the progressive damage law of the specimens obtained from the numerical scattering test. The results of the study can provide a theoretical basis for improving the bearing capacity of geopolymer and optimizing its structural performance. As well as reducing the impact of solid waste on the environment and improving the efficiency of resource use.

Study on seismic failure mechanism and damage model of unconstrained adobe block walls

Through the quasi-static cyclic in-plane loading test of three kinds of unconstrained adobe block walls, namely plain adobe wall, modified mud adobe wall and modified adobe wall, the failure mode and seismic performance of each specimen were clarified. Using residual deformation and cumulative energy dissipation as failure parameters, a two-parameter seismic damage model of unconstrained adobe block walls was established. and a calculation method for the adjustment coefficients of energy consumption items was provided. The results showed that the failure mode of the typical unconstrained adobe block wall under earthquake action was not affected by the modification of adobe materials, and the final failure mode was shear failure along the mud crack and the inclined crack extending through the block. Furthermore, the proposed seismic damage model can well reflect the evolution law of earthquake damage of adobe block walls, and the recommended damage index boundary values for five performance levels were given, providing a reference for performance-based seismic design and damage assessment of adobe block walls.

Mitigation of Fracturing Fluid Leak-Off and Subsequent Formation Damage Caused by Coal Fine Invasion in Fractures: An Experimental Study

During the hydraulic fracturing process of coalbed methane (CBM) reservoirs, significant amounts of secondary coal fines are generated due to proppant grinding and crack propagation, which migrate with the fracturing fluid into surrounding fracture systems. To investigate whether coal fines can form plugs to reduce fluid leak-off during the hydraulic fracturing stage, we conducted physical simulation experiments on coal seam plugging and unplugging to demonstrate that coal fines indeed contribute to reducing fluid leak-off during hydraulic fracturing. We also explored the plugging mechanisms of coal fines under different concentrations and particle sizes in fracturing fluids, and revealed the damage law of coal fines of temporary plugging on reservoir permeability. Research results indicate the leak-off volume of fracturing fluids containing coal fines is lower than an order without coal fines, demonstrating a significant effect of coal fines in decreasing fluid leak-off. The temporary plugging rate of coal fines increases with higher concentrations and decreases with larger particle sizes, achieving rates exceeding 90%. The high temporary plugging effect of coal fines results from the superposition of internal and external filter cakes. Under conditions of small particle size and high concentration, the damage to fractures during the fine return process is minimized. Considering the potential damage of coal fines to propping fractures and wellbore, the concentration of coal fines in fracturing fluids should be kept relatively low while ensuring a high temporary plugging effect. Overall, these findings provide crucial insights into optimizing the temporary plugging performance of coal fines during the hydraulic fracturing stage and controlling their behavior during the fracturing fluid flow-back stage, thereby enhancing reservoir fracturing effectiveness and improving CBM production rates.