Papers by Keyword: Kaiser Effect

Abstract: IIn the present study, Acoustic Emission (AE) monitoring technique is applied in order to characterize the brick masonry of two important military buildings located in Northern Italy: the barracks of Alessandria and Boves. The internal brick masonry walls of the two barracks object of the study are tested by two double flat-jack systems, in order to analyze the compressive strength of the structural material. Flat-jack testing is a versatile and powerful technique that provides significant information on the mechanical properties of historical constructions. The first applications of this technique on some historical monuments clearly showed its great potential. The flat-jack test method is only slightly destructive, and when double jacks are used, this test works according to the same principle as a standard compressive test. The difference is that it is performed in situ and the load is applied by means of two flat-jacks instead of the loading platens. During the tests, the stress-strain relationship of the masonry is determined by gradually increasing the pressure applied by the flat-jacks in the course of three loading-unloading cycles. Moreover, AE technique is coupled to the flat-jack testing, in order to assess the extent of damage in the masonry texture. Thus, AE technique makes it possible to highlight critical phenomena and fracture mechanics scale effects in the masonry by identifying the critical conditions, not entrusted to an analysis of the loading process (compression or shear), rather depending primarily on the distribution and evolution of crack patterns.

Abstract: 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.

Abstract: The research status of the rock acoustic emission technology had been discussed from three aspects, as the different status rock study, the processing technology study, the character analyzing technology study. The rock acoustic emission should be combined with the practical engineering, and to create effective rock acoustic emission processing and analyzing technology, to make the rock acoustic technology better adapted to the testing of the practical project.

Abstract: An edge chipping experiment under static load is adopted to study the Kaiser Effect during the failure process for engineering ceramics. The mechanisms inducing Kaiser Effect are discussed. Some AE signals during the course of Kaiser Effect are analyzed. The results show that there’s obvious Kaiser Effect during the failure process of edge chipping; count, energy and amplitude can be well used to describe the Kaiser Effect. The surface metamorphic layer remained on the ceramic surface during the course of machining is the main factor for Kaiser Effect. Edge distance and mechanics characteristic are the important factors for Kaiser Effect. The study on Kaiser Effect of edge chipping has provided some guidance to prevent edge chipping of engineering ceramics.

Abstract: High performance fiber-reinforced cement composites (HPFRCCs) show multiple cracks and a limited damage tolerance capability due to the debonding of the fibers of the cement matrix. For practical applications, it is necessary to investigate the fractural behavior of HPFRCCs to understand the mechanism of the microbehavior of a cement matrix containing reinforcing fibers. We have investigated the acoustic emission (AE) signals in HPFRCCs under monotonic and cyclic uniaxial compressive loads. Four types of specimen were tested. The experimental parameters studied were: the type of fiber (polyethylene or polyvinyl alcohol), the hybrid type (with steel cord), and the loading pattern. The data shows that the progress of the damage in HPFRCCs in the compressive mode is characteristic of the type of hybrid fiber and its volume fraction. From the AE data, the second and third compressive load cycles resulted in a successive decrease in the amplitude compared to the first compressive load cycle. In addition, an AE Kaiser effect was observed in HPFRCCs specimens up to 80% of their ultimate strength. These observations suggest that the AE Kaiser effect has potential for use as a new tool to monitor the loading history of HPFRCCs.

Abstract: In this research, the non-linear ultrasonic and acoustic emission techniques were used to evaluating damages induced in concrete under compression loading. Cubic concrete specimens were produced with three different w/c. The nonlinear ultrasonic evaluation was based upon measuring the change in fundamental amplitude with increasing damage and output power level. In acoustic emission testing technique 4 sensors were used to record the AE events under various loading and unloading cycles. An increase in AE hits was observed with increasing damage. Since concrete contains microcracks even under initial loading stages, none of the test specimens exhibited clear signs of the occurrence of Kaiser Effect. Normalized values of Felicity Ratio were plotted and compared with the nonlinear ultrasonic test data. A correlation between acoustic emission and nonlinear ultrasonic techniques in assessing damage growth in concrete was investigated.

Abstract: Kaiser effect was noticed while submitting marble samples to Brazilian tests. An automatic data acquisition system was applied by means of analog to digital conversion, upon recording analog signals of stress, strain and acoustic emission (AE) emitted from Portuguese marble specimens under diametrical loadings in different loading cycles. Results confirm that the Kaiser effect was pronounced and was easy to be detected under Brazilian tests with a felicity ratio varied from 0.92 to 1.09. This means it is possible to measure the pre-existing stresses in rocks under complex states of stress by means of other tests besides uniaxial compression. Results also show that cumulative AE events vs. stress curve is more suitable for Kaiser effect recognition than cumulative AE energy vs. stress curve as every event has different scales of energy.

Abstract: 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.

Abstract: The Kaiser Effect in acoustic emission is often used for an estimation of the stress to which rocks have been subjected. However, there are cases in which the Kaiser Effect is not clear, since the noises due to the contact and/or the stick slip between the pre-induced fracture surfaces are measured during the reloading process. In such cases, estimation of previous stress is difficult by the conventional method which is based on the acoustic emission activity observed under reloading process. In the tests for the Kaiser Effect on rocks, therefore, the noises must be eliminated from the acoustic emission generated from newly created cracks during the second loading process. Such techniques as analysis of the difference between the acoustic emission activity observed in the first and second reloading and the analysis of the change in the slope of the acoustic emission amplitude distribution have been proposed. In this paper we present a new method by which the maximum previous stress in rocks can be directly estimated without any post signal analysis. In the new method, simultaneous measurement of acoustic and electromagnetic emission during loading test of rock sample is employed. The electromagnetic emission in the deformation of rock sample generates only when the fresh surfaces due to cracking are created in the material, and the source of electromagnetic emission is the electrification between the fresh crack surfaces. This paper describes the simultaneous measurement of acoustic and electromagnetic emission useful for estimating the rock in-situ stress.