Damage Distribution Characteristics Research Articles

Study on the distribution characteristics of damage and multidimensional parameter influence of abrasive water jet impact on reinforced concrete

AbstractAbrasive water jet (AWJ) crushing technology holds significant promise for concrete maintenance and demolition. However, challenges such as high energy consumption and mismatched parameters require urgent optimization to enhance crushing efficiency. To address this, this paper proposes a novel method combining smoothed particle hydrodynamics (SPH) and the finite element method (FEM) to develop a numerical model for reinforced concrete (RC) subjected to AWJ impact. The study explores the damage distribution characteristics and the impact of various parameters on RC under AWJ conditions. The results reveal that the axial damage reduction in RC progresses through three stages: rapid reduction, slow reduction, and the slowest reduction. In contrast, the longitudinal damage reduction process consists of rapid and slow reduction stages. Furthermore, within the studied parameter range, the comprehensive damage factor of RC increases rapidly and then stabilizes as the jet velocity rises. As the nozzle diameter increases, the comprehensive damage factor initially decreases sharply and then increases rapidly. With increasing abrasive concentration and stand‐off distance, the comprehensive damage factor rises quickly before declining.

Study on ultrasonic lamb wave testing technology of honeycomb sandwich structures

Abstract Honeycomb sandwich composite panels have complex structures, large sizes, many types of defects, and significant sound attenuation, which lead to low efficiency and poor sensitivity of ultrasonic non-destructive testing. In the study, a non-linear ultrasonic lamb wave testing technique for honeycomb sandwich composite panels is proposed. Firstly, the anisotropic propagation characteristics and modal structure of lamb waves in honeycomb sandwich composite panels are analyzed, and the lamb wave modes with non-linear ultrasonic accumulation are excited. Secondly, the data extraction method and imaging algorithm of non-linear ultrasonic lamb wave imaging testing are proposed. Finally, an enhanced imaging algorithm is proposed to improve image quality based on the sliding window algorithm. Based on the comparative analysis of air-coupled ultrasonic testing images and metallographic tests, it can be seen that non-linear ultrasonic lamb wave testing signals can be used to characterize the damage distribution characteristics of honeycomb sandwich composite panels, display debonding and weak debonding defects, and have the advantages of being able to perform on the same side testing and high efficiency, which can be used for non-destructive testing of honeycomb sandwich composite panels.

Experimental study on decoupled charge blasting-induced crack propagation with parabolic shaped charge

In this study, a new parabolic shaped charge structure is proposed to realize bidirectional blasting in coal mines. To examine the fracture characteristics of rock mass induced by shaped charge structure under explosion load, a dynamic caustic experimental system is adopted. Further, the blasting-induced damage distribution characteristics of rock mass caused by different decoupling coefficients are investigated. Using polymethyl methacrylate (PMMA) as the experimental material, a two-dimensional model is established. AUTODYN, an explicit dynamics simulation program, is used to examine the initial crack generation process under shaped charge blasting. The stress wave propagation rule and the relationship between blasting damage and decoupling coefficient are explored. The results show that the parabolic shaped charge structure can control the explosion energy distribution and reduce the surrounding rock damage. When the decoupling coefficient is 2, the main crack length is optimum. During the crack propagation process, the growth rate and stress intensity factor of the main crack of the specimen show an oscillatory downward trend. Two stress concentration points are generated on either side near the main crack, forming the initial crack. When the decoupling coefficient is less than 2, long cracks exist in both the shaped and non-shaped charged directions, and the energy gathering effect is poor. When the decoupling coefficient is greater than 2, the energy gathering effect is obvious, but the main crack length is shorter.

Research on damage optimization of copper-carbon gradient composite materials for current-carrying friction

To meet the demand for damage optimization of current-carrying friction materials and based on the uneven distribution characteristics of damage, copper-graphite gradient composite materials were prepared using spark plasma sintering technology. These materials were paired with H62 brass, conducting damage optimization studies on copper-graphite gradient composite materials using a self-made current-carrying friction test machine. The results indicate that the copper-graphite gradient composite materials possess excellent current-carrying performance. With an increase of graphite content, the degree of mechanical damage and arc damage on the worn surface is optimized. The friction coefficient and wear rate of the material significantly decrease. When the content of graphite in the material is 5 wt% − 10 wt%, The material's damage optimization reaches the best and the wear rate is 9.7 × 10−4 mg·m−1. At this point, the predominant form of damage to the material is plastic deformation.

Study on damage mechanism and damage distribution of the rear plate under impact of debris cloud

The debris cloud generated by the hypervelocity impact (HVI) of orbiting space debris directly threatens the spacecraft. A full understanding of the damage mechanism of rear plate is useful for the optimal design of protective structures. In this study, the hypervelocity yaw impact of a cylindrical aluminum projectile on a double-layer aluminum plate is simulated by the FE-SPH adaptive method, and the damage process of the rear plate under the impact of the debris cloud is analyzed based on the debris cloud structure. The damage process can be divided into the main impact stage of the debris cloud and the structural response of the rear plate. The main impact stage lasts a short time and is the basis of the rear plate damage. In the stage of structure response, the continuous deformation and inertial motion of the rear plate dominate the perforation of the rear plate. We further analyze the damage mechanism and damage distribution characteristics of the rear plate in detail. Moreover, the connection between velocity space and position space of the debris cloud is established, which promotes the general analysis of the damage law of debris cloud. Based on the relationship, the features of typical damage areas are identified by the localized fine analysis. Both the cumulative effect and structural response cause the perforation of rear plate; in the non-perforated area, cratering by the impact of hazardous fragments is the main damage mode of the rear plate.

Mesoscopic damage characteristics of hydrophobicity-modified geopolymer composites under freezing-thawing cycles based on CT scanning

The mesoscopic damage characteristics of geopolymer under freezing-thawing (F-T) cycles affect its macroscopic physical and mechanical properties, which further influence the safety of geopolymer buildings. This paper presents a study on the mesoscopic damage characteristics of hydrophobicity-modified geopolymer composites (HM-GC) based on the CT scanning technique. The damage degree and damage distribution characteristics of geopolymer composites (GC) before and after hydrophobic modification were compared. The gradient distribution characteristics of damage caused by F-T cycles in HM-GC were further analyzed. The results show that the volumetric porosity of the GC is always larger than that of HM-GC under the same F-T cycle number, indicating the hydrophobic treatment can reduce the F-T cycle damage rate and damage degree. The results also show that the damage induced by F-T cycles in GC and HM-GC shows obvious spatial gradient characteristics. As the F-T cycle number increases, the average gradient coefficient of GC increases first and then decreases, while the average gradient coefficient of HM-GC increases first and then stabilizes. The hydrophobic treatment can reduce the gradient characteristics of the F-T cycle damage and improve the F-T durability of geopolymer composites.

Fractal study on the damage induced by shaped charge blasting with uncoupled eccentric charge

In this study, a dynamic caustic experimental system is used to examine the damage distribution characteristics as well as the crack formation/propagation mechanism in polymethyl methacrylate (PMMA) caused by uncoupled eccentric shaped charge blasting under different decoupling coefficients and charge positions. Using PMMA as the experimental material, the damage variables around the hole are calculated by the digital image processing method. The stress wave propagation law under different charge positions is revealed. Furthermore, based on the fractal theory, the damage values of shaped and unshaped cracks are calculated. The results show that the range of the crushed zone and failure zone on the coupled side around the hole of eccentric uncoupled charge is larger than that on the uncoupled side, which can reduce the damage on the reserved side and break the excavation side more fully. Under the condition of eccentric uncoupled charging, the range of the crack zone and failure zone decreases with the increase in the decoupling coefficient. When the decoupling coefficient is 2, the smoothness of the main crack is the best, and the total and average lengths of the main crack are also maximum. The damage distribution caused by explosive crack conforms to the fractal law, and the fractal dimension can accurately represent the damage degree of PMMA after the explosion.

Tunnel Lining Stability and Structural Damage Threshold under Seismic Loading

To analyze the damage distribution characteristics and ultimate bearing capacity of tunnel linings under seismic action, damage variables were introduced into the Mohr-Coulomb constitutive model. Thus, an incremental elastic–plastic damage constitutive model for concretewas constructed. Uniaxial tensile and compressive tests were performed to verify model reliability, and the damage thresholds for different strength classes of concrete under the test conditions were numerically obtained when destruction occurred. These damage thresholds were considered as the criteria for material failure to solve the ultimate bearing capacity and failure form of the tunnel structure. Calculation results demonstrate that as the peak ground acceleration increases, the shallowly buried tunnel structure presents the three following stages: elastic bearing, local instability, and overall instability. If the compression or tensile damage values of an element exceed the threshold value, the element is regarded as destroyed. The failure of any element of a structure can be used as a criterion for local instability. If the volume of the destroyed elements exceeds 10% of the overall volume of elements, and the proportion of destroyed elements in the lining shoulders and side walls begins to abruptly increase, the structure can generally be regarded as unstable.

The vibration propagation and damage distribution characteristics of deep-buried underground cavern blasting

With the increase of the scale of an underground cavern, more and more towering underground side walls are left behind by blasting operation, which leaves a huge hidden danger to the structure safety of an underground cavern. Taking the propagation mechanism and damage distribution characteristics of blasting vibration along the elevation direction as the research subject, the propagation mechanism of blasting vibration along the elevation direction of high side wall of a deep-buried underground cavern can be obtained by comprehensive application of theoretical analysis, dimensional analysis, formula derivation, numerical analysis, and other research methods. Through multiangle comparative analysis, the internal mechanism of blasting vibration under elevation effect in underground caverns is revealed, and combined with the relationship between surrounding rock damage and blasting vibration velocity, the distribution characteristics of blasting vibration and damage under the elevation effect are proposed. In addition, through the establishment of a mechanical model of the response of blasting vibration of underground high side walls, the prediction formula of particle vibration velocity along the elevation direction under blasting vibration condition is analyzed, and the formula is adjusted and modified, which can meet the developing requirements of surrounding rock damage control precision.

Model experimental study on strain field evolution and damage distribution of filling body under blast loading

Ensuring the stability of filling bodies is an important part of safe construction in the mining process of the filling body method in metal mines. As blast loading is one of the main external factors affecting the stability of filling bodies, it is of great significance to study the failure mechanism of filling bodies under blast loading for guiding the actual production. In this study, a self-made mould was used to develop a plane explosive loading model of an ore-filling body. Based on this model a Digital Image Correlation (DIC) technology-hyperdynamic strain synchronization test system was established, and the strain data collected by the two systems were compared. The results showed that the variation trend and peak strains of the two systems over time were consistent. Further, based on the DIC method and fractal theory, the ore diameter and explosive equivalent were selected as dependent variables to vary the blast loading strength, and the damage distribution characteristics and strain field evolution law of the filling body under different blast loading strengths were studied. The results showed that the filling body exhibited a single failure pattern of radial crack under low blast loading and a composite failure pattern of radial and circumferential crack under high blast loading. With the increase in the intensity of load, the radial crack number increased gradually. When the explosive equivalent was taken as a single variable, the damage degree of the filling body varied linearly with the explosive amount. Under the action of blast loading, the von Mises strain field in the filling body decayed exponentially along the radial direction from the explosion source. The change in blast loading intensity had a significant impact on the strain field close to the ore-filling interface but had less of an impact on the strain field farther away from the ore-filling interface. Specifically, when the initial load intensity of the filling body was high, the strain field near the interface of the filling body showed the characteristics of “high intensity and fast attenuation”, while the strain field intensity was low in the distant area. When the initial load intensity was low, the intensity of the full-field strain field in the filling body was low, exhibiting the change characteristics of “slow decay“.

Simulation of Magnetorheological Plane Polishing Scratch Creation Process and Suppression Method

This study was conducted to simulate the causes of, and suppress, the scratch damage on the workpiece surface during magnetorheological surface polishing. The molecular dynamics method combined with polishing contact trajectory modeling was used to simulate the scratch damage formation process, and the scratch damage morphology model was established by analyzing the scratch damage distribution characteristics in the magnetorheological plane polishing process. The effect of different process parameters on the scratch damage characteristics was predicted by simulation, and orthogonal experiments were designed to explore the preferred polishing process parameters that could suppress the scratch damage formation. Finally, it was further verified that the formation of scratch damage can be effectively suppressed by controlling the workpiece speed, polishing disc speed, and magnetic field generator speed, and adjusting the magnetic field eccentricity distance under the premise of ensuring the surface roughness and flatness of the workpiece.

Microstructure evolution and process optimization of molybdenum rods during loose tooling forging

Defects such as abnormal grain growth and cracking are easy to occur in the process of loose tooling forging of large-size molybdenum rods prepared by powder metallurgy. In this work, the forging process of molybdenum rods was simulated, which were heated to 1350 °C, and one end of them was subjected to loose tooling forging with deformation of 20%, 30% and 40%, and then they were subjected to secondary heating at 1200 °C, 1250 °C, 1300 °C and 1350 °C for 60 min. The microstructure of the molybdenum rods was characterized by optical microscope (OM), and the equivalent stress, equivalent strain and damage distribution characteristics of during the forging process were calculated by Deform-3D finite element software. The microstructure evolution law and crack formation mechanism during deformation were analyzed. The results show that when the two ends of the molybdenum rods were separately forged and heated, incomplete static recrystallization was easy to occur in the middle gradient deformation zone due to the uneven distribution of stress and strain, resulting in the abnormal growth of local grains. In the subsequent forging process, the surface of the molybdenum rods was cracked due to the excessive stress at the grain boundary of the coarse grains in the transition zone. The initial temperature and softening temperature of static recrystallization in tempering process were different with the deformation of molybdenum rods. Finally, the process optimization of molybdenum rods forging was put forward.

Model experimental study on the effects of in situ stresses on pre-splitting blasting damage and strain development

In the process of drilling and blasting in deep underground engineering, in situ stress is usually considered as an essential factor for blasting parameter design. To explore the effect of the in situ stress value and direction on pre-splitting blasting (PSB), the blasting failure characteristics of a rock mass under different stress conditions are experimentally simulated by applying vertical and horizontal uniaxial pressures and blasting load to gypsum specimens. First, fractal theory is implemented to study the influence of uniaxial pressure on crack propagation and distribution. Second, based on the digital image correlation method, the development of strain in the surrounding rock is revealed. Finally, the damage distribution characteristics of the specimens after blasting are studied by using the acoustic wave detection. The results indicate that the value and direction of uniaxial pressure have a significant influence on PSB. Hence, when the direction of uniaxial pressure is parallel to the blasthole layout, the crack path is relatively straight. The damage of gypsum specimens decreases with the increase in uniaxial pressure. The attenuation amplitude of the peak strain in the parallel direction with the distance is much smaller than that in the vertical direction. When the direction of the uniaxial pressure is perpendicular to the direction of blasthole layout, the damage of specimen after blasting is substantial and is not conducive to the formation of cracks.

Study on the breaking process and damage characteristics of abrasive water jet impacting concrete based on acoustic emission

The breaking process and damage distribution characteristics of concrete are the theoretical basis for improving the quality and safety of concrete impacted by abrasive water jet (AWJ) technology. Therefore, the process of AWJ impacting concrete is monitored online based on acoustic emission (AE) technology in this paper. The results show that the AE signals of AWJ impacting concrete have two peaks in frequency domain, the low frequency signals are generated by AWJ and the high frequency signals are generated by concrete breaking. The autoregressive (AR) model is used to estimate the power spectrum of AE signals. The variations of AWJ signals and concrete crushing signals in the impact process are analyzed based on the power of AE signal defined by the area under the power spectral density (PSD) curve. Through monitoring the development process of erosion hole inside the transparent materials impacted by AWJ, it is verified that the power of the concrete crushing signals after the formation of the erosion hole can reflect the penetration rate well. In addition, the damage characteristics of concrete specimens impacted by AWJ are studied in this paper by measuring the transverse ultrasonic velocity of the specimens before and after impact.

Incipient spallation of high purity copper under non-one-dimensional strain shock waves

A new spallation experimental method by using conical target is proposed. Based on the analysis of wave propagation, the basic principle of spallation experiment of conical target is discussed. Then incipient spallation of high purity (HP) copper under non-one-dimensional strain shock wave is studied experimentally by using a gas gun setup. The damage distribution characteristics and micro-mechanism of conical HP copper target are analyzed. The intrinsic relationship between the characteristics of free surface velocity profiles and damage evolution is explored. The results indicate that 1) continuous damage zones including different damage states appear in the conical HP copper target with initial spallation from the bottom of cone to the top of cone along the direction parallel to the cone surface, which is attributed to the spatial evolution of the amplitude and duration time of tensile stress in the conical target; 2) quantitative statistical analysis of damage inside conical HP copper target reveals that the nucleation and early growth of micro-voids are random, while the coalescence of micro-voids has significant localization characteristics; 3) the normal free surface particle velocity profiles with typical pull-back spallation signals at different locations of conical HP copper target are measured by multi-channel photon Doppler velocimetry. Comparing with the damage distribution characteristics, it is revealed that the spallation strength based on pull-back velocity is independent of damage, and is the critical nucleation stress of micro-voids. But the slope and amplitude of pull-back rebound velocity depend on damage evolution process, which relates to the change of damage evolution rate and stress relaxation caused by damage degree respectively.

Evaluation of Dynamic Behaviors and Damage Mechanism of Ancient Timber Architectures

An urgent is needed on the preservation of Chinese architectural heritages, since environmental and time impacts have been abating their structural resistance capability. It is of great importance in protecting and rehabilitating the ancient architectural culture of China to study the structural characteristics of ancient Chinese timber architectures. As a typical example of ancient timber architectures-Yingxian Wooden Pagoda in west of Shanxi Prince, the dynamic characteristics and damage mechanics of the tower are investigated experimentally and numerically by micro tremor measurements and means of finite-element-method (FEM). The micro tremor measurements are conducted on the tower (each floor) and the surrounding ground. From the micro tremor observation data, the predominant frequency of the surface ground and natural frequency, vibration mode and the damage distribution characteristics of the tower were evaluated. Based on the experimental studies, the tower is created by a delicate finite element model. And in order to simulate the mortise and tenon joint---bucket arches in the structure, which is a combination of a series of timber structures, a special beam-element group is developed. Numerical simulation of the seismic response of the tower shows that the second and third floors of the tower would be damaged more seriously than other floors for their severe stresses when acted by seismic loading. The present analysis of the tower shows the same phenomena. The results provide basis for repairing and reinforcing the ancient timber tower.

The GIS and analysis of earthquake damage distribution of the 1303 Hongtong M=8 earthquake

The geography information system of the 1303 Hongton M=8 earthquake has been established. Using the spatial analysis function of GIS, the spatial distribution characteristics of damage and isoseismal of the earthquake are studies. By comparing with the standard earthquake intensity attenuation relationship, the abnormal damage distribution of the earthquake is found, so the relationship of the abnormal distribution with tectonics, site condition and basin are analyzed. In this paper, the influence on the ground motion generated by earthquake source and the underground structures near source also are studied. The influence on seismic zonation, anti-earthquake design, earthquake prediction and earthquake emergency responding produced by the abnormal density distribution are discussed.

On the spatial characterization of damage evolution by a one-dimensional model

Damage diffusion, concentration and localization are investigated by introducing a small non-uniform initial damage in the material. Several parameters characterizing the local and global damage non-uniformities are defined mathematically, and relations are established between these parameters and the constitutive laws for damaged materials through a simple one-dimensional calculation. The influence of damage non-uniformity on the material failure is illustrated by a quantity termed rupture toughness, defined as the specific plastic work the material can absorb prior to failure. Six continuum damage models are examined for their damage distribution characteristics by means of this methodology. For rate independent processes under stress controlled loading, the damage models based solely on the effective stress, such as the models advanced by Broberg ( J. appi. Mech. 41, 809, 1974) and by Roussiler (contribution to the research of fracture of metals in the elastic-plastic fields. Thesis of Ecole Polytech., Univ. Paris, 1979), show damage localization at a relatively low damage level, and a global concentration on both damage and plastic deformation fields. The same features are incorporated in Gurson's model ( J. Engng Mater. Tech. 99, 2, 1977) provided void nucleation is ignored. As to the creep damage processes, the phenomenological theory of Kachanov ( Ivz. Akad. Nauk., S.S.R., Otd. Tech. Nauk., No. 8, 1958) shows a range of damage distribution behaviour according to the ranges of its parameters and initial damage distribution. Damage diffusion prevails for creep damage growth controlled by grain boundary diffusion ( Cocks and Ashby, Prog. Mater. Sci. 27, 189, 1982). For the creep damage processes controlled by surface diffusion ( Cocks and Ashby, 1982), however, damage localization occurs at an early stage of damage evolution.