Felicity Effect Research Articles

Impacts of Cyclic Loading and Unloading Rates on Acoustic Emission Evolution and Felicity Effect of Instable Rock Mass

Uniaxial cyclic loading‐unloading compression experiments with schemes of six loading rates and six unloading rates were carried out on the combined testing platform. Impact of loading and unloading rates on rock AE characteristics was revealed. Results show that increasing loading and unloading rates resulted in decreasing total AE rings in the entire rock deformation and failure process. Increasing loading rate decreased the AE rings at loading stages, and increasing unloading rate decreased the AE rings at unloading stages in the same cycle. Total AE counts had a negative linear relationship to the loading and unloading rates. The loading stage was the active period of the AE phenomena, and impacts of the loading rate on the AE characteristics were more apparent. Especially when the loading rate was greater than 2.0 kN/s, brittle failure of rock specimens became noticeable. After the cyclic load reached the uniaxial compressive strength of 1/3∼1/2 times, the rock Felicity effect became more obvious. With the increase of the loading rate, the Felicity ratio decreased in the elastic stage and increased a little in the plastic stage, whereas with the increase of the unloading rate, the Felicity ratio decreased gradually in the elastic stage and remained almost the same in the plastic stage.

Acoustic emissions and pressure stimulated currents experimental techniques used to verify Kaiser effect during compression tests of Dionysos marble

The damage development due to externally applied mechanical stress is a hot topic of interest involving several applications of everyday life, like civil engineering, monument restoration, construction evaluation and health monitoring. Repetitive loadings of brittle materials cause internal damages that gradually extend, leading to inevitable failures. Such processes are studied under the concept of the materials’ mechanical memory effect that is widely known as Kaiser effect. The Kaiser effect states that a structure will only suffer further internal damaging when exposed to applied stresses higher than previously encountered. Certain conditions lead to a violation of the Kaiser effect, known as the Felicity effect, quantitatively measured using the Felicity Ratio. This work presents the experimental results when repetitive mechanical load loops are applied on marble specimens, while concurrent Acoustic Emission (AE) and Pressure Stimulated Currents (PSC) measurements are conducted. The collected AE and PSC data are studied in combination with the mechanical data, like mechanical stress and strain, under the frame of the Kaiser effect. It is clearly seen that the Felicity ratio strongly depends on the stress range the material is subjected to, with regard to the elastic or plastic deformation region.

Effect of water ageing on the load-unload cyclic behaviour of flax fibre-reinforced thermoplastic and thermosetting composites

In the present work, twill flax fabrics-reinforced thermoplastic and thermosetting composites were subjected to water ageing in order to study its effect on their mechanical properties. Water ageing was conducted by immersing composite specimens into tap water at room temperature until saturation. To assess their mechanical behaviour, the aged composites were subjected to monotonic and load-unload tensile tests completed by Acoustic Emission (AE) recording. The AE records were analysed by the k-means unsupervised pattern recognition algorithm associated with the Principal Components Analysis (PCA) and the Silhouette index. In particular, the load-unload tensile tests highlighted a decrease of about 10% of the aged composites stiffness with respect to unaged ones at high loads. Besides, three classes of damage events were identified and assigned to the damage mechanisms. Finally, the mechanical behaviour of the aged composites is found to exhibit a significant Felicity effect synonymous of a substantial damage induced by water ageing.

Effect of Loading Rate on the Felicity Effect of Three Rock Types

Effect of Loading Rate on the Felicity Effect of Three Rock Types

Towards efficient acoustic emission testing of COPV, without Felicity ratio criterion, during hydrogen-filling

This paper concerns the nondestructive testing of composite overwrapped pressure vessels (COPV) via acoustic emission (AE) method, and more particularly Felicity effect (FE) and its ratio (FR) as pass/fail criterion. It investigates alternatives to FR since it requires an unload/load ramp. This is expensive, inconvenient, and impractical when testing and gas-filling are performed simultaneously. The investigations are achieved on a big volume COPV during a proof-pressure. The COPV was previously subjected to mechanical impacts at different energy levels and zones. Analysis of AE data in terms of zonal and planar localizations was performed. FR was investigated separately for each AE equipment channel. Results showed that the FE was followed, in the case of all sensors located near the impacted zones, indicating then the appearance of damage. It has been proven that COPV failure location was well correlated with a geographic region which had identified through zonal and planar localizations. Results showed also that in the case of the current experienced COPV, pass-fail criteria for in-service inspection during gas-filling operations (i. e. without unload/load ramp), can be based on zonal and planar localizations analysis in lieu of FR. Though FR is a good damage indicator which could support pass-fail criteria, it is not essential for real-time COPV testing during hydrogen filling, and alternatives could be found.

Acoustic emission during quench training of superconducting accelerator magnets

Acoustic emission (AE) sensing is a viable tool for superconducting magnet diagnostics. Using in-house developed cryogenic amplified piezoelectric sensors, we conducted AE studies during quench training of the US LARP’s high-field quadrupole HQ02 and the LBNL’s high-field dipole HD3. For both magnets, AE bursts were observed, with spike amplitude and frequency increasing toward the quench current during current up-ramps. In the HQ02, the AE onset upon current ramping is distinct and exhibits a clear memory of the previously-reached quench current (Kaiser effect). On the other hand, in the HD3 magnet the AE amplitude begins to increase well before the previously-reached quench current (felicity effect), suggesting an ongoing progressive mechanical motion in the coils. A clear difference in the AE signature exists between the untrained and trained mechanical states in HD3. Time intervals between the AE signals detected at the opposite ends of HD3 coils were processed using a combination of narrow-band pass filtering; threshold crossing and correlation algorithms, and the spatial distributions of AE sources and the mechanical energy release were calculated. Both distributions appear to be consistent with the quench location distribution. Energy statistics of the AE spikes exhibits a power-law scaling typical for the self-organized critical state.

Application of a novel optical fiber sensor to detection of acoustic emissions by various damages in CFRP laminates

In this research, we applied a novel optical fiber sensor, phase-shifted fiber Bragg grating balanced sensor with high sensitivity and broad bandwidth, to acoustic emission (AE) detection in carbon fiber reinforced plastics (CFRPs). AE signals generated in the tensile testing of angle-ply and cross-ply CFRP laminates were both detected by the novel optical fiber sensor and traditional PZT sensors. The cumulative hits detected by both sensors coincided after applying simple data processing to eliminate the noise, and clearly exhibited Kaiser effect and Felicity effect. Typical AE signals detected by both sensors were discussed and were tried to relate to micro CFRP damages observed via microscope. These results demonstrate that this novel optical fiber sensor can reliably detect AE signals from various damages. It has the potential to be used in practical AE detection, as an alternative to the piezoelectric PZT sensor.

Cooling cycle effects on low temperature cracking characteristics of asphalt concrete mixture

The effect of cooling cycles on the low temperature behavior of asphalt concrete mixtures is investigated using a recently developed acoustic emission (AE) test device. In an attempt to link the local AE response of the asphalt mixtures to the pavement global response obtained through mechanical tests, the AE-based results were validated using traditional mechanical pavement performance testing methods namely, the disk-shaped compact tension [DC(T)] test and the indirect tensile test (IDT) method. Field-aged pavement cores, which were expected to have a gradient in binder aging properties (more aging near the surface of the pavement), were collected and tested. Test results revealed that significant damage resulted from cyclic cooling, effecting the fracture energy and stress relaxation ability of the asphalt mixture. The AE results collected were consistent with the results obtained using the DC(T) and the IDT test methods. The so-called Felicity effect was observed by evaluating AE activity occurring in a sample subjected to multiple cooling cycles and an AE based healing index was introduced to evaluate the amount of healing that resulted from warming cycles. Low temperature induced microdamage was also investigated using X-ray computer micro-tomography, in an effort to better understand the physical nature of microcracking in asphalt mixtures at low temperatures and the source of AE emissions detected.

Damage accumulation behavior of non-crimp fabric-reinforced epoxy composite under static and cyclic tensile loading

A non-crimp fabric with a stacking sequence of [0°,+45°,90°,−45°] embedded in epoxy resin matrix was analyzed. Samples for mechanical test were obtained from laminates at different orientations depending on the textile architecture direction at 0°, 45°, and 90° in order to study the relationship between damage initiation and propagation with fabric geometry. Tension mode tests (static and cyclic) were carried out to evaluate the evolution of damage using as a main tool, the acoustic emission technique that allows monitoring the mechanical behavior of the materials during the test in ‘real time’. Results show that there is a remarkable mechanical influence of the reinforcement textile in the composite and that damage generation and progression (mechanisms of fracture) is highly dependent of the direction in which the stress is applied in relation with the architecture of the fabric. In static tensile mode, samples at 0° exhibited better mechanical parameters than samples at 90°, while at 45° orientation was lesser. The effect of textile geometry was demonstrated to have an influence in such mechanisms. In cyclic tensile mode, Kaiser effect is observed at low stresses, while the experimental results showed that the Felicity effect became clearer along with the increasing of stress level.

Research Status and Prospect of Concrete Acoustic Emission Technology

By discussing the current research status of the concrete acoustic emission technology from four aspects as: the concrete acoustic emission of different conditions; the characteristics of the concrete acoustic emission; the Kaiser effect and Felicity effect of the concrete acoustic emission and the analysis of the concrete acoustic emission data. The concrete acoustic emission research should be done with the practical project, and establish effective processing and analyzing technology of the concrete acoustic emission, to apply the concrete acoustic emission technology better to the measurement of real project.

고압가스 연료탱크의 손상평가를 위한 음향방출 변수의 분석

본 논문은 자동차용 type II CNG 연료탱크의 손상평가를 위하여 파열시험 중 발생하는 음향방출 변수의 분석에 관한 연구이다. 음향방출 신호의 kaiser effect, felicity effect 및 creep effect의 관찰과 전체 hits에서 진폭 60dB이상의 hits가 차지하는 비율 계산으로 연료탱크의 손상도를 평가할 수 있었으며, 평균 rise time, 평균 진폭 및 평균 initial, reverbration 주파수를 분석함으로써 압력용기의 손상메커니즘을 추정하였다. This paper described analysis of acoustic emission parameter for the damage evaluation of type II vehicle fuel tank during fracture test. The observation of Kaiser effect, Felicity effect and creep effect is the means of damage evaluation method. It is possible to evaluate tank damage by the ratio of hit of over 60 dB and total hit. Damage mechanism of pressure tank can be estimated by analysis of average rise time, average amplitude.

Effect of Yarn Sizes on the Tensile Damage Evolution of a C/SiC Composite Fabricated by Chemical Vapor Infiltration

The damage evolutions of C/SiC composites fabricated by chemical vapor infiltration with two different sizes of yarns were compared by cyclic tensile load/unload tests accompanied with the acoustic emission (AE) monitoring. The results show that an inflexion was observed in both the evolution of hysteresis characteristics and the corresponding AE curve for composite with fine yarns, which is, however, absent for composite with coarse yarns, suggesting that the former is much closer to the tough material than the latter one. Felicity effect was observed for both composites, which is more pronounced for the composite with coarse yarns due to the large yarn sizes leading to more matrix debris inside the yarns.

Effectiveness of nonlinear ultrasonic and acoustic emission evaluation of concrete with distributed damages

Nonlinear ultrasonic (NLU) and acoustic emission (AE) techniques are used for nondestructive evaluation of concrete, damaged under compression loading. Experiments were carried out in 18 cubic specimens (150 × 150 × 150 mm) cast with three different w/c (six specimens for each w/c). Three specimens at each w/c were used for AE monitoring and three others for NLU evaluation. The NLU evaluation is based on measuring the change in fundamental amplitude with increasing damage and output power level. In acoustic emission testing technique four sensors were used to listen to the wide range of events under various loading and unloading cycles. An increase in AE hits was observed with increasing damage. Each loading and unloading stage was carefully examined for Kaiser and Felicity effects in order to assess the concrete deterioration. It was proposed to measure Felicity ratio at three different loading levels, corresponding to AE hits at 3%, 5%, and 10% of the AE hits at the previous maximum load, respectively. Normalized values of Felicity ratio were plotted and compared with the NLU test data. Correlation between acoustic emission and nonlinear ultrasonic techniques in assessing damage growth in concrete was investigated.

Characterization of Tensile Damage for 3D-C/SiC Composites by Acoustic Emission

The various damage mechanisms in 3D-C/SiC composites are identified using acoustic emission (AE) signal parameters, and the Felicity effect is studied on different unloading stress. As a result, the damage mechanisms in 3D-C/SiC composites can be identified successfully by the amplitude, average frequency and relative energy, and there are several damage modes together during uniaxial tensile process. The Kaiser effect is almost absent and the Felicity ratio fluctuates at 0.95 on lower stress stage and drops when the relative stress is above 65%.

Violation of the Kaiser effect by hydraulic-fracturing-related microseismicity

Application of a load to different materials and rocks induces acoustic and seismic emission. If the load has a cyclic character, then as a rule such an emission will vanish for loads less than the maximum previously reached load level. This is the so-called Kaiser effect, which is an expression of memorized stress history of materials and rocks. Usually, this effect is assumed to be valid also in the case of fluid-induced seismicity. Here, we show that microseismicity occurring during hydraulic fracturing violates the Kaiser effect. In material sciences, such a breakdown of the Kaiser effect is termed the felicity effect. We observe that the felicity effect can be directly related to reopening of the hydraulic fracture forced by fluid injection in loading cycles. In contrast, closing of the hydraulic fracture following injection cessations seems to be governed by the Kaiser effect. We explain such a contrasting behaviour of microseismicity by an aseismic character of a slow fracture closing and by rubbing and pore pressure diffusion during a quick fracture reopening. This violation of the Kaiser effect for tensile fracturing due to hydraulic forcing on rocks is similar to the absence of this effect in the case of shear fracturing by seismogenic processes. Possibly, the felicity effect is a common feature of ongoing active faulting.

Experimental Verification and Theoretical Analysis on Felicity Effect of Acoustic Emission in Concrete

The experiment of acoustic emission (AE) on concrete specimens under uniaxial cyclic loading was conducted. The Kaiser effect of acoustic emission in concrete and the Felicity effect, which manifest the memorizing ability to the maximum previous stress level of Kaiser effect, were validated by the experiment. The mechanism of Felicity effect was analyzed based on the theory of statistical damage mechanics and a tentative AE factor constitutive model of brittle material under uniaxial cyclic loading was suggested. The curve of constitutive model is in good coincidence with the curve from the experiment. The experimental results showed that the Felicity effect became clearer along with the increasing of stress level. Each loading cycle would cause new damage inside the material, and the response of material to the new loading cycle is different from the previous cycle.

Studying Unloading Failure Characteristics Of A Rock Mass Using The Disturbed State Concept

Because of coal seam excavation and periodic disturbance of back-and-forth coal cutting, the surrounding rock is subjected to tiered cyclic unloading and loading. Based on this, a seepage experiment under constant axial stress and tiered cyclic unloading-loading confining pressure was carried out, and two new damage variables were proposed. These results showed that, the accumulative plastic deformations and corresponding permeability increased step-wise with unloading levels, permeability decreased with cycle number in the same unloading level when the unloading level was small, it was the opposite when the unloading level was large. The Kaiser effect and the Felicity effect actually coexisted during the experiment. As the unloading level increased, the relationship between dissipated energy and cycle number converted from logarithm to linear relationship. Two damage variables showed that the critical value of the damage variables for coal failure Dc≈0.9.

An investigation of acoustic emission from an irradiated nuclear graphite

Acoustic emission (AE) responses from unirradiated nuclear graphites subject to cyclic loading have been shown to exhibit the Felicity effect, i.e., AE is detected at stresses below the previous peak stress. This has been attributed to time dependent recovery processes which occur upon unloading and at zero stress [1]. This paper describes work comparing similar unirradiated and irradiated nuclear sleeve graphites. The number of AE event counts from irradiated graphite was shown to be greater than that from unirradiated graphite, subjected to similar stresses. This effect was attributed to the increase in porosity caused by radiolytic oxidation. A Felicity effect was observed on cyclic loading of irradiated graphite, but no evidence for a Kaiser effect was found for irradiated graphite loaded monotonically to failure. The absence of a Kaiser effect can be attributed to relaxation and recovery processes that occur in the considerable time interval between removing the irradiated graphite from the reactor and post-irradiation examination. Therefore, it was concluded that AE monitoring is not a suitable technique for measuring internal stresses in irradiated graphites.

Creep and recovery in graphites at ambient temperature: An acoustic emission study

Nuclear graphites subject to compressive or tensile stress cycling show a Felicity effect, that is, acoustic emission (AE) is detected at stresses less than the previous peak stress. This is attributed to recovery processes that occur upon unloading and at zero stress. The extent of recovery increases with time (up to 10 5 mins) at zero stress between cycles. For two graphites (IM1-24 and PGA) held under constant compressive or tensile strain, AE over ∼16 h is attributed to creep. For the same graphites at zero stress (after application of a compressive or tensile prestress), AE over ∼16 h is attributed to creep recovery. Both types of AE time curve follow logarithmic rate laws similar to those derived earlier for high-temperature primary creep and creep recovery. The micromechanical processes that give rise to creep and AE on loading graphites are basal plane shear and microcracking; creep recovery is attributed to the reverse of these processes.

Acoustic emission responses from cyclic loading of a nuclear graphite

An analysis is presented of acoustic emission from samples of a nuclear graphite, IMI-24, subjected to three consecutive, load-unload cycles to 5, 10, and 15 MPa, in tension, compression, and flexure. On the first cycle, cumulative acoustic emission events in all loading modes increased progressively from zero stress. However, in subsequent cycles, acoustic emission recurred at stresses approaching, but less than, the previous peak stresses (i.e., a Felicity effect was observed rather than a Kaiser effect). A new parameter, the Recovery ratio, B, is proposed for characterizing the pattern of acoustic emission on cyclic loading of graphites.