Kaiser Effect Research Articles

Earth concrete under cyclic loadings: Stress-strain curves and damage assessment by means of acoustic emission and digital image correlation techniques

Cyclic compressive tests were conducted on recycled sand (RS) earth concrete mixtures of different amounts of clay conserved previously at wet and dry curing conditions (relative humidity (RH) = 90% and 50%, respectively). The loops of the stress-strain curves were analyzed. In addition, Kaiser Effect investigation and acoustic emission (AE) damage assessment were carried out. The evaluation showed a successful correlation between the AE indices and cracking progression which was captured by means of digital image correlation (DIC) technique. The results reveal that Kaiser Effect was achieved at wet curing condition whereas it was not attained at the dry one. The RS specimen of highest clay content at dry curing condition demonstrated the highest degree of damage. In line with the journal's aims and scope and as a novelty, this paper finally examines Kaiser Effect by means of DIC. The results revealed that this aspect which is known to be linked with damage occurrence is not necessarily affected by the evolution of crack width.

Cosmological-scale Lyα Forest Absorption around Galaxies and AGNs Probed with the HETDEX and SDSS Spectroscopic Data

We present cosmological-scale three-dimensional neutral hydrogen (H i) tomographic maps at z = 2–3 over a total of 837 deg2 in two blank fields that are developed with Lyα forest absorptions of 14,736 background Sloan Digital Sky Survey (SDSS) quasars at z = 2.08–3.67. Using the tomographic maps, we investigate the large-scale (≳10 h −1 cMpc) average H i radial profiles and two-direction profiles of the line-of-sight (LOS) and transverse directions around galaxies and active galactic nuclei (AGNs) at z = 2–3 identified by the Hobby–Eberly Telescope Dark Energy eXperiment survey and SDSS, respectively. The peak of the H i radial profile around galaxies is lower than the one around AGNs, suggesting that the dark matter halos of galaxies are less massive on average than those of AGNs. The LOS profile of AGNs is narrower than the transverse profile, indicating the Kaiser effect. There exist weak absorption outskirts at ≳30 h −1 cMpc beyond H i structures of galaxies and AGNs found in the LOS profiles that can be explained by the H i gas at ≳30 h −1 cMpc falling toward the source position. Our findings indicate that the H i radial profile of AGNs has transitions from proximity zones (≲a few h −1 cMpc) to the H i structures (∼1–30 h −1 cMpc) and the weak absorption outskirts (≳30 h −1 cMpc). Although there is no significant dependence of AGN types (type 1 vs. type 2) on the H i profiles, the peaks of the radial profiles anticorrelate with AGN luminosities, suggesting that AGNs’ ionization effects are stronger than the gas mass differences.

Experimental study on acoustic emission stress memory function of rock-like specimens under uniaxial compression

The Kaiser effect in rock acoustic emission (AE) test is the most direct manifestation of rock memory function. This article focuses on the influence of different deformation stages and different historical stress conditions on stress memory function, and conducts AE testing of rock-like specimens. It explained the stress memory function in AE testing from the perspectives of crack propagation and damage accumulation. The crack initiation stress σci and crack damage stress σcd of specimens were obtained based on the stress-strain curve method, and the different deformation stages were divided. The damage evolution coefficient [Formula: see text] was proposed to measure the size of the stable development range of damage based on the normalized crack initiation and crack damage stress. The historical stress in the elastic stage could be easily identified from the Kaiser effect during the reloading process, even if the time interval reached 120 hours. The Felicity effect appeared during the reloading process when the historical stress was in the stage of stable crack propagation, and the FR value showed a decreasing trend with the extension of the time interval between loading tests. The loading history in the elastic stage was a training for the AE stress memory function under complex historical stress conditions, which restored the Kaiser effect in the stage of stable crack propagation. The distribution of AE events and CT scanning results were also analyzed in the article, and the damage accumulation information characterized by both are basically consistent. The double Kaiser effect phenomenon appeared in the AE test under complex historical stress conditions, although the criterion for discriminating the AE signal at the Kaiser effect point corresponding to the lower stress remained to be further studied and verified.

Acoustic Emission Behavior of TATB Based PBX during Uniaxial Compression Deformation

In order to study the feasibility of acoustic emission technology for the damage and fracture monitoring of TATB-based PBX materials and components, the acoustic emission characteristics of notched and unnotched specimens under uniaxial compression were studied. The results of uniaxial compression and step-cycle compression experiments of unnotched specimens showed that there were few AE hits with low amplitude under low strain stage and many AE hits were generated when the specimen failed. In addition, the Kaiser effect is applicable at the low load stage. In addition, there were less AE hits in initial loading stage for the specimen with notches, which may be caused by machining force. However, very strong AE hits were generated in the specimen with notches before macroscopic fracture occurred. Acoustic emission technology can be used to determine whether macroscopic cracks were generated in TATB-based PBX structures in the experiment.

The Effect of Specimen Size on Acoustic Emission Parameters and Approximate Position of Defects Obtained during Destructive Testing of Cementitious and Alkali-Activated Degraded Fine-Grained Materials.

Two sizes of test samples were selected to investigate the effect of size on the level of degradation. The smaller test specimens had dimensions of 40 × 40 × 160 mm, and the larger ones had dimensions of 100 × 100 × 400 mm. Both sizes of test specimens were always made of the same mortar. In one case, Blast Furnace Cement was chosen as the binder. In the other case, it was an alkali-activated material as a possibly more environmentally economical substitute. Both types of material were deposited in three degrading solutions: magnesium sulphate, ammonium nitrate and acetic acid. The reference set was stored in a water bath. After six months in the degradation solutions, a static elastic modulus was determined for the specimens during this test, and the acoustic emission was measured. Acoustic emission parameters were evaluated: the number of hits, the amplitude magnitude and a slope from the amplitude magnitude versus time (this slope should correspond to the Kaiser effect). For most of the parameters studied, the size effect was more evident for the more degraded specimens, i.e., those placed in aggressive solutions. The approximate location of emerging defects was also determined using linear localisation for smaller specimens where the degradation effect was more significant. In more aggressive environments (acetic acid, ammonium nitrate), the higher resistance of materials based on alkaline-activated slag was more evident, even in the case of larger test bodies. The experiments show that the acoustic emission results agree with the results of the static modulus of elasticity.

Research on the Characteristics of Acoustic Emission Activities of Granite and Marble under Different Loading Methods

Abstract At present, there is no corresponding standard for the engineering application of rock acoustic emission technology. To better apply acoustic emission technology to engineering practice, in this paper, the acoustic emission characteristics of different rock samples of marble and granite under uniaxial compression were analyzed by indoor acoustic emission test, the factors affecting the acoustic emission characteristics of rocks are studied, and the failure mechanism and damage characteristics of rock are discussed. The research contents include analyzing the curve fitting relationship between the acoustic emission event rate, the number of events, the stress time, and study of the similarities and differences of acoustic emission characteristics of marble and granite; analysis of damage characteristics of marble and granite based on acoustic emission parameters; by analyzing the relationship between the Felicity ratio of different rocks and the stress level during cyclic loading, the applicability of studying the Kaiser and Felicity effects of rocks; variation of acoustic emission event rate and rock peak intensity under different loading methods and loading rates. The results show that the acoustic emission of marble and granite has experienced the initial compaction zone, the rising zone, the peak zone, and the falling zone, and the two kinds of rocks have different acoustic emission phenomena in different stages, and the duration of each stage is also different; before the instability of the two kinds of rocks, there is a quiet period of acoustic emission, and the higher the rock strength, the longer the duration of this quiet period, which means that the calm period can be used as a precursor feature of rock mass instability for disaster prediction; during the cyclic loading process of rock, the damage development law is divided into three stages: initial stage, stable stage, and instability stage. When the Kaiser effect did not appear for the two rock stresses before 20%, between 20% and 70% of the peak strength, the Kaiser effect is obvious. When the stress exceeds 80% of the peak value, the Kaiser effect fails, and the Felicity effect appears; the variation of the loading rate affects the variation of the acoustic emission event rate, and the increase of the loading rate leads to aggravated rock damage. The theoretical stress-strain curve can reasonably reflect the actual stress-strain characteristics of rock by combining the number of acoustic emission events with the rock damage model. The results are consistent with the acoustic emission test, which verifies the inevitable relationship between acoustic emission and damage to the rock.

Constitutive model for simulating the mechanical behaviour of rock under triaxial cyclic loading

To simulate the cyclic behaviour of rock comprehensively, relevant mechanical features were analysed sufficiently, including the massing effect, ratcheting effect, Kaiser effect and Felicity effect. A constitutive body was proposed based on the deformation mechanism and implemented by strain increment method. This body comprised three elements (elastic element Ee, plastic element Ep and friction element Ef), in which Ee and Ep were connected in series, and Ef was connected with them in parallel. Two kinds of triaxial cyclic loading experiments were conducted to determine the constitutive laws of these elements and the Poisson’s ratios of Ee and Ep; moreover, the simulation effect was validated against the experimental data. Results showed that the tangential modulus of Ee was nonlinear due to damage development and variation of particle dense state, the backwards movement of the yield surface involving Ep during reloading induced the ratcheting effect and Felicity effect, and the opposite role of Ef during loading and unloading caused the massing effect. The constitutive laws of Ee and Ep could be expressed by quadratic polynomial function and logistic equation, respectively; the Poisson’s ratio variations in Ee and Ep with axial plastic strain could be expressed by linear function and exponential function, respectively.

Stress‐Based and Convolutional Forecasting of Injection‐Induced Seismicity: Application to the Otaniemi Geothermal Reservoir Stimulation

AbstractInduced seismicity observed during Enhanced Geothermal Stimulation at Otaniemi, Finland is modeled using both statistical and physical approaches. The physical model produces simulations closest to the observations when assuming rate‐and‐state friction for shear failure with diffusivity matching the pressure build‐up at the well‐head at onset of injections. Rate‐and‐state friction implies a time‐dependent earthquake nucleation process which is found to be essential in reproducing the spatial pattern of seismicity. This implies that permeability inferred from the expansion of the seismicity triggering front (Shapiro et al., 1997, https://doi.org/10.1111/j.1365-246x.1997.tb01215.x) can be biased. We suggest a heuristic method to account for this bias that is independent of the earthquake magnitude detection threshold. Our modeling suggests that the Omori law decay during injection shut‐ins results mainly from stress relaxation by pore pressure diffusion. During successive stimulations, seismicity should only be induced where the previous maximum of Coulomb stress changes is exceeded. This effect, commonly referred to as the Kaiser effect, is not clearly visible in the data from Otaniemi. The different injection locations at the various stimulation stages may have resulted in sufficiently different effective stress distributions that the effect was muted. We describe a statistical model whereby seismicity rate is estimated from convolution of the injection history with a kernel which approximates earthquake triggering by fluid diffusion. The statistical method has superior computational efficiency to the physical model and fits the observations as well as the physical model. This approach is applicable provided the Kaiser effect is not strong, as was the case in Otaniemi.

Impact dynamic characteristics and constitutive model of granite damaged by cyclic loading

To study the influence of damage degree on dynamic characteristics of damaged rock mass, the samples with different damage degrees were obtained by cyclic loading test and then the impact failure test was carried out by a 100-mm diameter split Hopkinson pressure bar (SHPB) device. In addition, the Zhu-Wang-Tang (ZWT) constitutive model was improved to establish the dynamic constitutive model of damaged granite. Results show that when the cyclic upper limit stress (CULS) reached 60% of the compressive strength of rock mass, the Felicity effect was significant and the Kaiser effect basically disappeared. Furthermore, there was obvious compressive strengthening effect of damaged rock mass under impact load, with the increase of the CULS in the early stage, the dynamic compressive strength of granite samples showed an overall decreasing trend. The damage degree had a significant effect on the propagation and energy absorption ability of rock mass, thus affecting its failure characteristics. Eventually, the proposed constitutive model was fitted with the experimental data, which showed that the model could accurately describe the dynamic mechanical properties of damaged granite under impact load.

Estimation of stresses in a massive granite using laser ultra-sonic testing and stress memory effect

This paper addresses in-situ stress-estimation methods based on the Kaiser effect. The physical and mechanical properties of granite, diorite, and granodiorite samples selected at different depth intervals of the core obtained from a wellbore were examined. The ultimate uniaxial compressive strength, modulus of elasticity, and Poisson’s ratio of the rock samples were determined using presses and strain gauges. Also, local longitudinal and shear wave velocities were measured using a high-accuracy laser-ultrasonic system with a view to assessing the structure of the samples. Based on the resulting elastic wave velocity maps, samples with no obvious discontinuities were chosen. These undisturbed samples were subjected to uniaxial compression and their acoustic emission was simultaneously measured. In-situ stresses were estimated from the results of the interpretation of acoustic emission measurements. The experimental in-situ stresses were compared with the results of a numerical simulation. The ratio of the estimated in-situ stresses to the calculated ones is within the range from 0.81 to 1.11. This means that the laser ultrasonic and acoustic emission methods make it possible to effectively estimate in-situ stresses in a rock mass and assess the degree of rock mass damage.

Minkowski Tensors in Redshift Space—Beyond the Plane-parallel Approximation

The Minkowski tensors (MTs) can be used to probe anisotropic signals in a field, and are well suited for measuring the redshift-space distortion (RSD) signal in large-scale structure catalogs. We consider how the linear RSD signal can be extracted from a field without resorting to the plane-parallel approximation. A spherically redshift-space distorted field is both anisotropic and inhomogeneous. We derive expressions for the two-point correlation functions that elucidate the inhomogeneity, and then explain how the breakdown of homogeneity impacts the volume and ensemble averages of the tensor Minkowski functionals. We construct the ensemble average of these quantities in curvilinear coordinates and show that the ensemble and volume averages can be approximately equated, but this depends on our choice of definition of the volume average of a tensor and the radial distance between the observer and field. We then extract the tensor Minkowski functionals from spherically redshift-space distorted, Gaussian random fields and gravitationally evolved dark matter density fields at z = 0 to test if we can successfully measure the Kaiser RSD signal. For the dark matter field, we find a significant, ∼10% anomalous signal in the MT component parallel to the line of sight that is present even on large scales R G ≳ 15 Mpc, in addition to the Kaiser effect. This is due to the line-of-sight component of the MT being significantly contaminated by the Finger of God effect, which can be approximately modeled by an additional damping term in the cumulants.

Damage assessment of reinforced concrete structures under elevated-amplitude cyclic loading using sentry values based on acoustic emission testing

ABSTRACT This article reports the combined application of sentry value and the Gaussian Mixture Modeling (GMM) algorithm to study crack classification in reinforced concrete (RC) beams using acoustic emission (AE) testing. The AE generated from RC beam specimens subjected to elevated-amplitude cyclic loading was used to study crack classification. The specimen approaches yielding, followed by a structural failure, when AE hits linked with shear cracks begin to exceed AE hits associated with tensile cracks. The sentry value for RC beam specimens decreased with subsequent higher amplitude loading phases, indicating the formation of macrocracks. The Kaiser effect phenomenon in RC beams was observed. The yielding of steel rebars and subsequent collapse of the RC beam specimens, followed by unstable crack propagation, were identified using the zero-slope line and a vertical spike in the sentry value versus the time graph. The current study appears to be significant for damage assessment and crack classification of in-situ RC flexural members.

Study on the mechanism of mechanical property strengthening of Beishan granite under mild temperature condition

Many researches found that mechanical properties of granite were strengthened under the mild temperature range (within 300 °C), which is positive for the long-term safety of the high-level radioactive waste (HLW) geological disposal engineering. To study the thermal strengthening mechanism of granite under elevated temperature by the decay heat of the HLW, a novel experiment was carried out which stress loaded firstly to cause stress damage, then thermal loaded to study the temperature effect on stress damaged granite. Results show: (1) the deformation memory effect and the Kaiser effect existed after stress loaded for non-thermal treated and 120 °C treated on granite, while the deformation memory effect (DME) was significantly faded after 250 °C treated. (2) The volume of pores/cracks in Beishan granite increased after stress loaded, then decreased significantly after 120 °C and 250 °C treated. (3) The deformation behavior, AE activity and pores/cracks closure all showed that the stress induced damage could be healed at elevated temperature, which is positive for the HLW disposal engineering. (4) A viscoelastic frictional sliding model was used to analyze the mechanism of DME fading and the mechanical property strengthening.

Thermoacoustic emission characteristics and real-time damage evolution in shales of the Lower Palaeozoic Niutitang Formation

Identifying shale geological temperatures is important for understanding the thermal maturity, thermal evolutionary history, and hydrocarbon generation stages of shale formations, and enables efficient shale gas development. This paper investigates the thermal Kaiser effect of shales under different warming rates by studying the thermoacoustic emission (TAE) characteristics of shales in the Lower Palaeozoic Niutitang Formation in the Micangshan area of China. The developmental evolution and microscopic response mechanisms of different types of fractures in shales under high-temperature conditions are explored by combining acoustic emission (AE) characteristic parameters. The memory and sensitivity of the thermal Kaiser effect were also verified by thermal fatigue tests. The results show that there is a significant thermal Kaiser effect during the heating of shale and that its threshold temperature is approximately 180 °C, which is consistent with the palaeotemperatures based on bitumen reflectance (Rb) estimation. The heating rate does not have a significant effect on the threshold temperature. At high temperatures, the shale is dominated by small-scale tensile fractures. When the shale is heated to 300 °C, the organic matter reaction rate peaks and the proportion of shear cracks begins to increase. An increase in heating rate is beneficial to the development of large-scale tensile cracks, while inorganic minerals begin to expand due to heat and micro-cracks gradually expand and connect, thus improving the connectivity of the pore channels. In thermal fatigue tests, the shale retains its memory of the threshold temperature when heated to less than 300 °C. Above 300 °C, pyrolysis of organic matter and microcrack expansion interfere with the thermal Kaiser effect, causing the shale to lose its memory of the maximum temperature. Within the same cycle stage, the threshold temperature is significantly higher at high heating rates than at low ones, especially above 400 °C.

Stress intensity factor evolution considering fracture process zone development of granite under monotonic and stepwise cyclic loading

Quasi-brittle materials like rocks may present mechanical non-linearity during cylic loading due to the formation of fracture process zone (FPZ), which poses a challenging task for accurate measurement of stress intensity factor (SIF). Understanding the crack development and SIF evolution under cyclic loading is beneficial for clarifying the mechanism of rock fatigue failure. Crack initiation and propagation are observed in semi-circular bending granite specimens subjected to monotonic and stepwise cyclic loading. Digital image correlation (DIC) and acoustic emission (AE) techniques are used to quantify the fracture behaviors through deformation fields and AE characteristic parameters. With the measured displacements around the notch, a novel J-integral method is coded and adopted to quantify the SIF at the crack tip which inherently takes the FPZ into account, and its validity is verified with synthetic images. Experimental results indicate that the development of the FPZ and SIF under cyclic loading is more complex than that under monotonic loading. The FPZ length, the SIF, and the crack opening displacement increase with the number of cycles in a specific loading level. For the loading level with a smaller upper load limit, the FPZ and SIF increase stably under repeated cycles, and AE events cluster in the first few cycles, exhibiting a significant Kaiser effect. As the upper load limit of the loading level increases, the FPZ and SIF increase linearly with the number of cycles, and the increase in the AE count rate and amplitude indicates the occurrence of abundant energetic microcracks under repeated loads. When the SIF at the crack tip approaches the fracture toughness of granite, the accelerated growth of the SIF in the last few cycles is accompanied by a rapid crack extension, resulting in a sharp rise in cumulative AE counts and energy.

Retracted: A Simple and Accurate Interpretation Method of In Situ Stress Measurement Based on Rock Kaiser Effect and Its Application

Retracted: A Simple and Accurate Interpretation Method of In Situ Stress Measurement Based on Rock Kaiser Effect and Its Application

Experimental study on fracture properties of dam concrete under post‐peak cyclic loading based on DIC and acoustic emission techniques

AbstractIn order to study the fracture properties of dam concrete under post‐peak cyclic loading, wedge splitting tests with three loading rates were performed on notched cubic specimens. Meanwhile, the acoustic emission (AE) and digital image correlation (DIC) technologies were used to monitor crack propagation in the specimens. As the loading rate increases, the peak load increases, and stiffness degradation increases. The cumulative AE counts show a step increasing trend and exhibit a Kaiser effect, which decreases via the post‐peak cyclic loading procedure and increases as the loading rate increases. The AE energy fluctuates markedly, and b value fluctuates frequently with an increasing loading rate. As the loading rate increases, the strain recovery rate decreases, and the permanent crack increases. The effective crack length gradually and steadily increases, and as the loading rate increases, the growth rate of the effective crack length increases.

The Kaiser effect in sedimentary rocks on the example of deposits of the Vertoletnaya area in Tomsk region

The acoustic emission memory effect (Kaiser effect) discovered in 1953 by the German scientist Joseph Kaiser is widely used as one of the methods of non-destructive testing of materials. In addition, according to acoustic emission data, it is possible to estimate the level of stresses experienced by rocks in reservoir conditions. In this paper, we consider the results of recording acoustic emission in sedimentary rock samples from the Mesozoic part of the section of Western Siberia. The studying features of the manifestation of acoustic emission signals was carried out on the main lithological varieties (medium-grained sandstone, mudstone, siltstone, sandstone with carbonate cement). In total, 43 samples were analyzed under uniaxial loading and 1 sample under pseudo-triaxial loading. The results of the study are graphs of the dependence of the total number of acoustic emission signals from the stress. The dependence of the number of acoustic emission signals on the group of sedimentary rocks is determined.

Progressive damage and tensile failure of open‐hole carbon fiber polymer composites reinforced by carbon nanotubes

AbstractProgressive damage and tensile failure of open‐hole carbon fiber/carbon nanotube reinforced composites with different off‐axis angles were detected by acoustic emission and Micro‐CT. K‐mean clustering algorithm can be utilized to post‐process signals of acoustic emission. Three critical points including linear growth point, near maximum load point and failure point, were selected to study progressive damage. Results indicated that stiffness variable decreased with the increase of off‐axis angle. When the off‐axis angle was 0°, higher initial stress and catastrophic brittle fracture characteristics can be obtained, whereas pseudo‐ductile behavior can be observed when off‐axis angles were 30° and 45° because of the alignment of yarn (fiber trellising) and the matrix plasticity. Due to the symmetrical structure of plain texture, there was a very interesting phenomenon that the tensile strength of composite specimen with 45° off‐axis angle was 23.65% higher than that of the specimen with an off‐axis angle of 30°. In the second stage of loading, the slope drop sharply when the load reached first key point, and Kaiser Effect can be observed. Acoustic emission technology and Micro‐CT method are beneficial to damage assessment of complex composites.

Directional independence of the Kaiser effect of sandstone with high diameter–thickness ratios

The Kaiser effect(KE) was investigated considering strain energy density factor theory in fracture mechanics and the formation mechanism of the independence of effect direction.The results were as follows: Felicity ratio (FR) increased with increasing rotation angle, indicating that the memory of the original rock stress was affected by the rotation angle. Thus, the directional independence of the KE was directly related to the rotation angle. In theoretical calculations, the directional independence of the KE was directly related to the relative value of critical stress. The change in the relative value of the critical stress increased the difficulty of cracking, affecting the accuracy of the KE point.Poisson’s ratio considerably affected the FR value, and the in situ stress values of the KE method on various types of rock samples differed. The results of the study can provide insight into the KE mechanism and development of effective methods.