Search Results (20)

During the production, storage, and use of solid rocket motors, the impact generated by unexpected accidents, such as collision or drop, will cause damage to the propellant and affect the safety of the motor. However, the progressive evolution mechanism of mesoscopic damage in NEPE propellant under such impact conditions has not been fully elucidated, and there is still a lack of quantitative method to evaluate the impact-induced damage degree, which restricts the engineering safety assessment of solid rocket motors. To investigate the influence mechanism, the mesoscale damage characteristics of NEPE propellant under drop-weight impact is systematically studied. First, damaged NEPE specimens are obtained by conducting drop-weight experiments with a 10 kg hammer, where the drop height is varied to apply different impact impulses. The internal meso-structure of the propellant is then characterized using micro-CT, yielding detailed imagery of the refined meso-structural features and damage morphologies in the NEPE propellant. To capture the dynamic evolution process of mesoscale damage, a mesoscopic model incorporating AP, Al, HMX particles and voids, is subsequently constructed based on the high-precision mesoscopic morphology characterized by micro-CT. By integrating the deviatoric constitutive model, Gurson plastic damage model, and bilinear cohesive zone model, high-fidelity numerical simulations of the drop-weight impact damage process are performed using the advanced SPH-FEM coupling algorithm. The results indicate that no significant damage occurs when the impact impulse is less than 13.85 N·s. As the impulse increases, phenomena including matrix microcracks, void collapse, particle/matrix interface debonding, and main crack formation appear sequentially. When the impulse exceeds 24.25 N·s, particle fragmentation and transgranular fracture occur, accompanied by plastic flow and frictional heating that induce ignition. Finally, the overall damage degree is fitted by the Boltzmann function, and a function for quantitatively describing the damage degree is obtained, which can provide theoretical support for the impact safety assessment of solid rocket motors. Full article

Impact-damaged reinforced concrete (RC) columns often experience significant reductions in load-carrying capacity and ductility when subjected to subsequent axial loading. Carbon fiber-reinforced polymer (CFRP) sheets have been widely used to strengthen such damaged columns; however, the underlying strengthening mechanism remains insufficiently understood, largely due to the difficulty of experimentally capturing the evolution of internal damage. To address this issue, a three-dimensional (3D) meso-scale finite element (FE) model has been developed to investigate the mechanical behavior of CFRP-strengthened impact-damaged RC columns. The proposed model captures the evolution of micro-damage within concrete and provides a more realistic representation of impact-induced damage compared with conventional homogeneous models. The model was first validated against available experimental results, showing good agreement in both failure modes and responses. Based on the validated model, three typical strengthening schemes, including the longitudinally applied CFRP, U-shaped CFRP, and fully wrapped CFRP, are systematically examined in terms of failure patterns, load-carrying capacity, stiffness, ductility, and energy dissipation. The results indicate that the fully wrapped CFRP configuration most effectively mitigated damage in the impact-affected zone and increased the load-carrying capacity by up to 86%. Furthermore, a quantitative evaluation framework based on strengthening indices for axial capacity and energy dissipation is proposed, indicating that strengthening with two CFRP layers can lead to a desirable ductile failure mode within the scope of this numerical investigation. These findings provide useful mechanistic insights into the strengthening process and offer preliminary guidance for the rehabilitation of impact-damaged RC columns, though further validation is required before practical implementation. Full article

Taking the Daliang Tunnel of the Lanzhou–Xinjiang High-speed Railway crossing a reverse strike-slip fault as the engineering background, seismic damage investigations of the Daliang Tunnel and other cross-fault tunnels under earthquake action were conducted. Using 1:50 meso-scale model tests, experimental analyses were carried out on the lining strain response, internal crack development and failure, and surrounding rock pressure variation during fault dislocation. The failure modes and mechanisms of tunnels crossing reverse strike-slip faults were thoroughly explored. Meanwhile, a three-dimensional numerical model of the Daliang Tunnel was established to investigate the influence of dislocation modes with structural zonation within the fault zone on the surrounding rock response. The results indicate that the damage and strain response of the tunnel lining are mainly distributed within the fracture zone, predominantly characterized by combined oblique shear and compression failure. Due to the displacement of the lining induced by strong surrounding rock movement, surrounding rock pressure exhibits considerable variation at the boundaries of the fracture zone, accompanied by certain void detachment phenomena. The overall deformation of the tunnel crossing the reverse strike-slip fault presents an “S”-shaped pattern, which is consistent with the numerical simulations. The compression and dislocation morphology of the sidewalls within the rupture surface is in good agreement with the point cloud plan view. The compressive deformation and strain of the surrounding rock are most significant within the rupture surface. Meanwhile, the soft-to-hard transition segments between the new fracture zone and the rupture surface, as well as between the rupture surface and the influence zone, exhibit a trend of first decreasing and then increasing. Full article

Water level fluctuations in reservoir areas subject bank slopes to intense wet–dry cycles (WDCs), compromising rock mass stability. This study investigates the macro–meso damage evolution of yellow sandstone from the Wudongde Reservoir. Specimens subjected to 0–20 WDCs were analyzed using nuclear magnetic resonance (NMR) alongside Brazilian splitting, uniaxial, and triaxial compression tests. Results indicate that porosity increases linearly with WDC, rising from 6.12% to 17.61% after 20 cycles, driven by the transformation of micropores into macropores. Macroscopic mechanical parameters, particularly tensile strength and cohesion, exhibit significant exponential and sharp decay, respectively, while the internal friction angle remains relatively stable. Notably, increasing confining pressure effectively mitigates WDC-induced deterioration by inhibiting microcrack propagation. The damage mechanism is primarily attributed to the dissolution of clay binder and uneven mineral swelling/shrinkage, whereas the rigid mineral skeleton remains largely intact. These findings provide a theoretical basis for quantifying rock damage and predicting slope stability in complex hydrological environments. Full article

Polypropylene fibers provide an innovative solution for enhancing the crack resistance of tunnel lining segments. However, existing macro-models obscure the distinct effects of fibers on the mortar and ITZ, while explicit meso-modeling remains computationally prohibitive. This study develops a multi-scale modeling framework to investigate PFRC segment fracture under bending. The framework integrates a 3D meso-scale module for calibrating fracture-related material properties, a 3D macro-scale module for predicting global displacements, and a 2D meso-scale module for resolving local fracture processes. A full-scale bending test was performed to validate the framework and to examine the effects of fiber content at both scales. Both the full-scale test and numerical simulations show that the segment response exhibits three stages: elastic, damage development, and cracking at the design load. Numerical simulations further reveal that an optimal fiber content of 0.4% reduces the vertical displacement at the load point by 9.8% and the horizontal displacement at the edge point by 2.9% relative to the fiber-free case. Meso-scale simulations show that 0.4% fibers decrease the bottom crack width from 0.0868 to 0.0770 mm (−11.29%) and limit internal crack connectivity. Although fibers may locally promote ITZ cracking due to reduced mortar–aggregate bonding, a strengthened mortar matrix suppresses crack penetration and connected crack networks. A pronounced high-damage peak in the ITZ near the failure threshold confirms the ITZ as the governing weak link; therefore, further improvements may require ITZ-strengthening strategies. Full article

Building structures are inherently susceptible to damage from extreme dynamic loads, while conventional concrete exhibits inadequate tensile resistance. While hybrid fibers systems can surpass the limitations of single-fiber reinforcement through their synergistic action, their internal damage mechanisms under impact loading remain inadequately understood. This study investigates the dynamic splitting behavior of hybrid fibers-reinforced cementitious composites combining polyvinyl alcohol (PVA) with either steel (SF) or polyethylene (PE) fibers, using Split Hopkinson Pressure Bar (SHPB) tests at strain rates of 5–31 s⁻¹, along with industrial CT scanning for meso-scale damage analysis. Results indicate that the SF–PVA hybrid improved strength by up to 15.6% compared to mono-PVA, while the PE–PVA hybrid achieved an 11.1% increase. All hybrid systems exhibited improved energy dissipation (which rose 25–45% with strain rate) and displayed secondary stress peaks. Quantitative CT analysis revealed distinct damage patterns: the mono-PVA specimen developed extensive damage networks (porosity: 7.20%; crack ratio: 4.48%), the SF-PVA hybrid system displayed the lowest damage indices (porosity: 3.29%; crack ratio: 1.76%), whereas the PE-PVA hybrid system exhibited the most significant dispersed damage pattern (crack-to-pore ratio: 39.32%). The hybrid systems function via distinct mechanisms: SF–PVA offers multi-scale reinforcement and superior damage suppression, whereas PE–PVA enables sequential energy dissipation, effectively dispersing concentrated damage. These insights support tailored fiber hybridization for impact-resistant structural design. Full article

For the purpose of precisely depicting the failure and deformation of mudstone at varying burial depths under engineering activities, a statistical meso-damage constitutive model of mudstone was established on the basis of continuum damage mechanics, with the adoption of the compound power function and the Mohr–Coulomb yield criterion. Through triaxial compression tests under diverse confining pressures, the validity of this constitutive model was verified, and the macroscopic effects of mudstone damage evolution induced by internal defects and alterations in meso-structures were analyzed. The results reveal that an increase in confining pressure can remarkably enhance both the peak strength and the residual strength of mudstone. The constitutive model demonstrates relatively high accuracy in predicting the stress–strain responses, as well as the residual strength of mudstone. Moreover, parameter ε0 is capable of reflecting the macroscopic deformation strength of mudstone. Specifically, the larger the value of parameter ε0 is, the greater the peak deviatoric stress of mudstone will be, accompanied by a stronger bearing capacity. Parameter m, on the other hand, governs the brittle-to-ductile transition characteristics under failure. It also demonstrates that the macroscopic brittle failure characteristics of mudstone will become more noticeable as the value of parameter m increases. Full article

Non-invasive sensing techniques have become a cornerstone in the study and preservation of Cultural Heritage. These techniques offer a means to investigate the internal structure and surface properties of precious and delicate objects without causing damage. This article is the second of three review articles exploring contact and non-contact imaging methods applied to Cultural Heritage at various scales encompassing micro- (i.e., manufacts), meso- (sites), and macro-scales (landscapes). The unifying factor of these techniques is their ability to infer variations in geometrical and physical properties across inspected surfaces or volumes. This allows researchers to discover new historical sites, map their spatial extent, and characterize their material features at different scales, from landscapes to artifacts. This second part focuses on the meso-scale, encompassing the inspection, documentation, study, and characterization of historical and archeological sites, monuments, and submerged sites, using both contact and remote sensing techniques. Full article

Red sandstone is widely distributed in southern China. Due to the significant difference in mechanical properties before and after hydration and its poor water stability, red sandstone often triggers landslide accidents. In this paper, red sandstone from an open pit slope in Jiangxi Province was taken as the research object. Two variables, namely the initial saturation degree (25%, 50%, 75%, and 100%) and the number of wetting–drying cycles (0, 10, 20, 30, and 40), were set. With the help of nuclear magnetic resonance, the Brazilian disc test, and fractal theory, the relationships among its meso-structure, macroscopic fracture mechanics characteristics, and deterioration mechanism were analyzed. The research results are as follows: (1) Wetting–drying cycles have a significant impact on the pore structure and fracture mechanics characteristics of red sandstone. Moreover, the higher the initial saturation degree, the more obvious the deterioration effect of the wetting–drying cycles on the rock mass. (2) After further subdividing the pores according to their size for research, it was found that sandstone is mainly composed of mesopores, and the deterioration laws of different types of pores after the wetting–drying cycles are different. The porosities of total pores and macropores increase, while the proportions of mesopores and micropores decrease. The fractal dimensions of macropores and total pores of each group of rock samples are all within the range of 2–3, and the fractal dimension value increases with the increase in the number of wetting–drying cycles, showing significant and regular fractal characteristics. Micropores and some mesopores do not possess fractal characteristics. The fractal dimension of rock samples basically satisfies the rule that the larger the pore diameter, the larger the fractal dimension and the more complex the pore structure. (3) Both the type I and type II fracture toughness of rock samples decrease with the increase in the number of cycles, and the decrease is the most significant when the initial saturation degree is 100%. After 40 cycles, the decreases in type I and type II fracture toughness reach 23.578% and 30.642%, respectively. The fracture toughness is closely related to the pore structure. The porosity and fractal dimension of rock samples and their internal macropores are linearly negatively correlated with the type II fracture toughness. The development of the macropore structure is the key factor affecting its fracture mechanics performance. (4) After the wetting–drying cycles, the internal pores of red sandstone continue to develop. The number of pores increases, the pore diameter enlarges, and the proportion of macropores rises, resulting in internal damage to the rock mass. When bearing loads, the expansion and connection of internal cracks intensify, ultimately leading to the failure of the rock mass. The research results can provide important reference for the stability analysis of sandstone slope engineering. Full article

A three-dimensional meso-scale numerical model, which considers (1) the concrete meso-structures, (2) the bond slip between concrete internal structures and steel bars, and (3) the stripping behavior of carbon fiber reinforced polymer (CFRP) cloth from the surface of the concrete component, is established to investigate the effects of concrete strength and the CFRP cloth ratio on the shear performance of reinforced concrete (RC) beams. On the basis of verifying the rationality of the shear failure model and the feasibility of the CFRP reinforcement simulation method, 30 orthogonally designed numerical models of six kinds of concrete strength and five kinds of CFRP cloth ratios were designed and established. Based on the numerical simulation results, this paper analyzes the damage evolution of the CFRP–concrete interface, the variation trend of CFRP strain along the height direction of beam, the failure mode, and the load-displacement curve. Results show the following: (1) With the increase of concrete strength grade and CFRP cloth ratio, the shear strength of RC beams strengthened with increases in CFRP cloth ratio, the influence range of concrete strength grade is 24–50%, and the influence range of the CFRP cloth ratio is 10–25%; (2) The improvement range decreases, and the improvement range of the concrete strength grade decreases, and the reduction range is about 20%; (3) Based on the simulation results, influences of concrete strength and CFRP cloth ratio on the shear strength of CFRP cloth-strengthened RC beams are quantitatively considered. Full article

In this paper, a series of experimental and numerical studies were carried out to investigate the effect of multiple cracks on concrete fracture behavior. Seven groups of double-crack concrete three-point bending (TPB) experiments with different crack lengths and different crack distances were carried out. The experimental results showed that the bearing capacity of double-crack specimens was slightly larger than the standard specimen with one central crack. Additionally, with an increase in the second crack length or with a crack distance reduction, the concrete’s bearing capacity increased correspondingly. Based on the experiments, a numerical meso-model was developed based on applying cohesive elements. The aggregate, mortar, interface transition zone (ITZ), and potential fracture surfaces were explicitly considered in the model. In particular, cohesive elements were used to characterize the mechanical behavior of the ITZ and potential fracture surfaces. A modified constitutive concrete model was developed by considering the potential fracture surfaces’ damage relation and friction effect. The accuracy of the developed meso-model was validated through a comparison between simulation and experiments. Based on meso-models, the influence of multiple cracks on the concrete bearing capacity was investigated by analyzing the energy evolution. The analysis results showed that the bearing capacity has a linear relation with the proportion of mode II energy consumption during the fracture process, which explains why specimens with multiple cracks have a slightly larger bearing capacity than the standard specimens. In summary, this study has found that in three-point bending fracture tests primarily characterized by mode I fractures, the presence of multiple cracks near the main crack slightly enhances the load-bearing capacity of the specimens. This is attributed to a slight increase in internal energy dissipation associated with the presence of these multiple cracks. Full article

Calculation and characterization of the whole process of internal microscopic damage to surface damage in red-bed soft rock is a theoretical research difficulty and an urgent need for engineering safety protection. However, the current study cannot accurately and directly correlate internal and external damage. Therefore, in this paper, a coupled tensor–DEM–FEM model is proposed to deal with surface damage by indoor triaxial test digital image processing (DIC), internal damage by FJM acoustic emission study, and internal and external damage by moment tensor correlation. The study demonstrates that the whole process damage process of the red-bed soft rock peak front can be divided into six distinct phases, with early damage beginning with the elastic phase; the local strain divergence value begins to spiral out of control during the period of crack acceleration development; the overall acoustic emission intensity distribution is in the range of [−8.5, −6.3] in two dimensions and in the range of [−11, −9] in three dimensions; the R were between −40 and 40, which corresponded to the results of the indoor tests. A model has been developed that allows a direct reflection of the whole damage process. The method can be used to better understand the disaster mechanism and guide engineering practice. Full article

The effect of freeze–thaw (F–T) in the seasonal frozen area would lead to damage to asphalt pavement. After water enters asphalt pavement, the water in voids would expand at a lower temperature, which could change the void content and number, affecting the macro mechanical properties of the asphalt mixture. The rapid development of CT scanning and digital image processing (DIP) provides powerful technical support for the research of asphalt mixture meso volume characteristics. In this paper, the mechanical properties of basalt fiber reinforced asphalt mixture subjected to F–T cycles were tested at different temperatures to clarify the decay law of mechanical properties under F–T cycles. Then, the meso images of the asphalt mixture under various F–T cycles could be obtained by using CT tomography. Based on DIP technology, the meso characteristic parameters of CT images for asphalt mixture were extracted, and the development of asphalt mixture freeze–thaw damage was further analyzed. The test results showed that with the F–T cycle, the macro mechanical properties of the asphalt mixture rapidly declined in the early stage of the F–T cycle and gradually tended to be flat. There would be serious damage inside the asphalt mixture in the late stage of the F–T cycle. The damage to the mechanical properties of the asphalt mixture under the F–T cycle can be attributed to the change in the internal mesostructure of the asphalt mixture. Based on the grey relational analysis theory, the formation of the connected void was the main factor affecting the damage in the early stage of the F–T cycle, while the formation of new voids mainly affected the later development of F-T damage. Full article

A meso-micro analysis technique established on the basis of micro-mechanics of failure in combination with progressive-based damage criteria of the composite material constituents (i.e., fiber and matrix) is demonstrated to predict the impact and compression after impact (CAI) performance of biaxial composite laminates. Damages in the composite material constituents are calculated using different failure models. The analysis technique is then used to investigate the impact and CAI behavior of 45° biaxial composite laminates, for both thermoset and thermoplastic resin systems. The results were presented in the form of damage propagation contours for both impact and compression after impact and a comparison of graphs showing displacement-time, internal energy-time, velocity-time, and contact force-time for both thermoset and thermoplastic resin. Full article

To achieve more accurate prediction of the potential failure location and to conduct a deeper analysis of the failure mechanism of concrete constructions, it is critical to probe the evolution process of internal meso-cracks that bear various intensities of load. While a computer Tomography (CT) test provides a non-destructive detection technique for obtaining the internal meso-damage state of concrete, traditional image processing and Digital Image Correlation (DIC) are ineffective in extracting meso-damage information from concrete CT images. On the other hand, by observing the shape change law of concrete’s internal holes under load, it is proposed to use the hole roundness and area fraction formula, developed based on the stereology principle and morphology, to characterize and predict the potential failure location. Four features particularly addressed include the CT image as a whole, image equal partitioning, crack and non-crack areas, and representative holes. The approach is to explore the variation law of critical hole shape parameters, especially the hole roundness under different loading stages, and analyze the relationship between the change in hole shapes and the final macro-crack positions. It is found that compared with the average area fraction, the average hole roundness value of cross section images is more sensitive to the change in stress. In both uniform partitioning and non-uniform partitioning, the average hole roundness value near the final macro-crack location exhibits an increase trend with the stress, while the smoothing effect caused by the hole roundness averaging always exists. Near the final macro-crack location, the roundness of each individual hole is positively associated with the stress, while away from the final macro-crack location such a relation may not be observed. This trend expounds the evolution process of meso-damage in concrete, and the finding can be used to predict the accurate locations of macro-cracks. Full article