1,720,991 research outputs found
Ultrasonic pulse velocity test for non-destructive investigations of historical masonries: an experimental study of the effect of frequency and applied load on the response of a limestone
No full textThe ultrasonic pulse velocity (UPV) method can be conveniently used for non-destructive testing of physical–mechanical properties of the stones within historical masonry, as well as to check the state of damage and microcracking. Before to proceed with in situ measurements, it is important to assess the contribution that both intrinsic characteristics of the stones and external factors may give to the ultrasonic response. In this work the effect of different wave frequencies, sample geometry and application of a compression load on the response of a natural stone to UPV test has been investigated. An extensive experimental campaign in laboratory conditions was carried out on a soft limestone, used in the historical building heritage of the Southern Italy. A negligible UPV dispersion was found at the used frequencies of 1 MHz, 120 and 55 kHz when a compression load was not applied; the measured velocities were found to be influenced by the stone inhomogeneity rather than by the sample size. They showed a slight decrease and still negligible dispersion under load up to the visible damage. Dispersion increased with the cracking progression. This indicates that enhanced capability of UPV, in checking material quality and damage conditions, can be obtained by combining the use of different wave frequencies. © 2016, RILEM
Ultrasonic and sonic techniques applied to concrete and masonry structures
No full textThe quality assurance during and after construction of new structures and after refurbishments, the characterization of material properties and damage due to time and environmental influences are more and more becoming a serious concern. In recent years, innovative Non Destructive Testing (NDT) techniques, applicable for the assessment of existing civil structures, have become available for in situ analysis on concrete and masonry structures, but they are still not established for regular inspections. In addition, in the civil engineering field, repairing and anti-corrosion protection of the building structure is one of the most important applications of polymer composites. Nonetheless, the adhesion between overlays and concrete or masonry substrate is a concerning factor affecting the reliability and durability of repair. During the change of environmental conditions (temperature and humidity) after curing, the need exists for adhesion monitoring in the case of large area objects like industrial floors, bridge decks, injected concrete structures. In this chapter two main objectives will be discerned. The first relates to the application of sonic and ultrasonic testing techniques to measure in situ the development in time of the mechanical properties of concrete and polymer composite. The second deals with the assessment of damage and defects in concrete or masonry, and between concrete or masonry and applied polymer composite by means of sonic and ultrasonic techniques. Different data acquisition procedures and methodologies together with example applications will be described including tomography, scanning acoustic microscope, transmission and surface measurements. Further, an impact-echo example application on post-tensioned concrete will be described. The importance of data visualisation in form of 2-D images will be discussed. All these are monitoring techniques that can be applied in situ after their validation in laborator
Analysis of CFRP joints by means of T-pull mechanical test and ultrasonic defects detection
No full textDefects detection within a composite component, with the aim of understanding and predicting its mechanical behavior, is of great importance in the aeronautical field because the irregularities of the composite material could compromise functionality. The aim of this paper is to detect defects by means of non-destructive testing (NDT) on T-pull samples made by carbon fiber reinforced polymers (CFRP) and to evaluate their effect on the mechanical response of the material. Samples, obtained from an industrial stringer having an inclined web and realized with a polymeric filler between cap and web, were subjected to ultrasonic monitoring and then to T-pull mechanical tests. All samples were tested with the same load mode and the same test configuration. An experimental set-up consisting of a semiautomatic C-scan ultrasonic mapping system with a phased array probe was designed and developed, optimizing control parameters and implementing image processing software. The present work is carried out on real composites parts that are characterized by having their intrinsic defectiveness, as opposed to the previous similar results in the literature mainly obtained on composite parts with artificially produced defects. In fact, although samples under study were realized free from defects, ultrasonic mapping found defectiveness inside the material. Moreover, the ultrasonic inspection could be useful in detecting both the location and size of defects. Experimental data were critically analyzed and qualitatively correlated with results of T-pull mechanical tests in order to better understand and explain mechanical behavior in terms of fracture mode. © 2018 by the authors
Evaluation of concrete strength by means of ultrasonic waves: A method for the selection of coring position
No full textThe evaluation of the concrete properties in a structure has a fundamental importance for safety and structural integrity assessments. An adequate knowledge of the structural concrete performances can be obtained from a large number of cores where performing destructive tests. Non-destructive ultrasonic waves test can be performed before other kind of tests, allowing to improve the assessment of the structural concrete performances and to extend the results to the same kind of elements of the structure, not directly investigated by destructive tests. The aim of this work is to test a new method to identify a good practice to select the position of testing points on which extract the cores starting from an analysis of a preliminary campaign of non-destructive measurements. In this way it is possible to reduce risk of errors of the compressive strength evaluation by a different approach from those used nowadays. The data obtained from an experimental campaign with both non-destructive and destructive tests on 75 concrete columns were considered to validate the new method. The implications of a completely random choice and the guided choice, using the method proposed, were analysed with an iterative and exhaustive approach. European Standard (EN 13791) was followed for in situ measurements and preliminary data analysis. © 2014 Published by Elsevier Ltd
Non destructive assessment of in situ concrete strength: comparison of approaches through an international benchmark
No full textStrength assessment of concrete in existing structures is a key issue. Many non destructive techniques (NDT) are available which can provide information about the material condition and several approaches can be used to derive strength estimates from NDT test results. However, common practice suffers from many drawbacks: (a) it is difficult to ascertain the level of accuracy/confidence of concrete strength estimates, (b) one lacks established guidelines for estimating the concrete strength variability, (c) the best way to combine NDT methods and coring remains an open issue. The RILEM TC 249 “Non destructive in situ strength assessment of concrete” is addressing these problems. A benchmark was carried out in order to compare (a) how experts define and can carry out an NDT investigation program and (b) how experts derive strength values from the NDT measurements. The benchmark was based on synthetic simulations which reproduced a synthetic data set corresponding to a grid of twenty 3 m-high columns defining a single-storey building structure. The comparison of the various strategies and the analysis of results enabled identification of the most influential parameters that define an investigation approach and influence its efficiency and accuracy. A special emphasis was placed on the magnitude of the measurement error. A model of the investigation strategy is proposed, that will be detailed in future guidelines. The reader is invited to refer to a companion paper (Alwash et al. in Mater Struct, 1. doi:10.1617/s11527-016-0962-x), based on more extensive Monte-Carlo simulations of the same case-study, which analyzes and quantifies the efficiency of the investigation strategies with respect to both average strength and strength variability assessment, in order to draw conclusions based on rational analyses rather than on the element of chance. © 2017, RILEM
"Uso della microscopia acustica per la valutazione del danneggiamento in provini sollecitati a fatica"
No full textApplication Ultrasonic Wave Propagation on the Cure Monitoring of Epoxy Adhesives for Restoration of Concrete
No full text
Ultrasonic pulse velocity test for non-destructive investigations of historical masonries: an experimental study of the effect of frequency and applied load on the response of a limestone
No full textThe ultrasonic pulse velocity (UPV)
method can be conveniently used for non-destructive testing of physical–mechanical properties of the stones within historical masonry, as well as to check the state of damage and microcracking. Before to proceed with in situ measurements, it is important to assess the contribution that both intrinsic characteristics of the stones and external factors may give to the ultrasonic response. In this work the effect of different wave frequencies, sample geometry and application of a compression load on the response of a natural stone to UPV test has been investigated. An extensive experimental campaign in laboratory conditions was carried out on a soft limestone, used in the historical building heritage of the Southern Italy. A negligible UPV dispersion was found at the used frequencies of 1 MHz, 120 and 55 kHz when a compression load was not applied; the measured velocities were found to be influenced by the stone inhomogeneity rather than by the sample size. They showed a slight decrease and still negligible dispersion under load up to the visible damage. Dispersion increased with the cracking progression. This indicates that enhanced capability of UPV, in checking material quality and damage conditions, can be obtained by combining the use of different wave frequencies
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