NDT Methods Research Articles

Ultrasonic NDT determination of initial and final setting time of cement paste

There are several methods for determination of the setting and early hardening in the cementitious composites. The most common method is using the Vicat apparatus. The major disadvantage of this method is that it is invasive and therefore the measurement results exhibit high variability. The paper deals with the continual monitoring of the process of setting and early hardening of a cement paste using the ultrasonic measurement. The innovative method of using the ultrasonic NDT method for determination of the setting times of cement paste is presented in the paper.

Comparison between air-coupled ultrasonic testing and active thermography for defect identification in composite materials

ABSTRACT Glass or carbon fibre-reinforced polymer (FRP) structures have attained a relevant role in modern production thanks to their lightweight, high resistance to corrosion and fatigue, and relative ease of manufacturing complex shapes. Nevertheless, several types of defects, such as voids, matrix fractures, delaminations and impact damages, which might significantly reduce the useful life of composite-made structural components, are often difficult to be identified. Conventional non-destructive methods, such as ultrasonic testing, are routinely used to monitor composite constructions with good results. However, an inspection of large structures requires alternative and faster NDT methods. Among these, air-coupled ultrasonic testing (ACUT) and active infrared thermography (AIRT) are generally considered the most promising ones. In this paper, ACUT and AIRT have been compared by performing experimental tests on two reference composite panels with synthetic defects. Polytetrafluoroethylene (PTFE) and aluminium inserts with different sizes and located at various depths have been used as artificial defects. The relative merits and drawbacks of the two techniques have been highlighted in terms of defect size sensitivity, maximum depth that can be detected, and thermo-physical properties of the reflector. A qualitative and quantitative analysis has been carried out to evaluate the ability of the two techniques in retrieving the actual size of the subsurface defects.

Introduction to the Examination of Thin-Walled Structures Using the Vibrodiagnostic Method

Abstract The article presents a methodology of non-destructive diagnostic vibratory tests of welded plates with geometrical parameters that classify them into a group of thin-walled panels. On the basis of such plates, most ship constructions are created. In previous works, the authors dealt with the study of welded joints in plates with significant thicknesses and developed for them a number of methods for assessing the quality of welded joints. Vibrodiagnostics is a NDT method that allows the use of a variety of techniques and tools. It enables measurements to be made in both a contact and non-contact way depending on the requirements of the structure and the environment. Vibrodiagnostic method is one of the most modern NDT methods, which uses modern measurement tools and computer analysis of data. On the basis of the developed methods, the authors intend to verify their application to plates from real welded constructions, which will be performed in typical shipyard conditions by welders. Such tests are important due to their use for the construction of a real SHM ship construction monitoring system. These methods allow for the examination of the condition of ships’ structural plates and can detect defects in welded joints that prevent ships from operating under severe sea conditions. The article presents the laboratory stand, the sensor layout, results, and their initial analysis.

A Comparison of Composite Specimens Damage area Measurements Performed using Pulsed Thermography and Ultrasonic NDT Methods

Abstract Carbon fiber reinforced plastics (CFRPs) are widely used in aerospace structures due to their high stiffness, strength and good fatigue properties. They are however vulnerable to loads perpendicular to their plane and, while impacted, can suffer significant internal damage decreasing their overall strength. Detecting and sizing such damage is an important task of the non-destructive inspection (NDI) methods. This study was conducted to detect and quantify damage in a set of six impacted even rectangular CFRP specimens designed from a MiG-29 vertical stabilizer’s skin. The inspection was done using the ultrasonic (UT) method (based on mobile scanner – MAUS V) and the pulsed infrared thermographic (IRT) method. Each specimen’s inside and outside (impacted) surface was inspected separately with IRT, while the outside surface was then inspected with UT. UT provided the most precise measurements of the damage area, while the IRT inspection of the outside surface (which would be accessible on a real aircraft structure) provided underestimated values due to the damage’s depth and geometry.

Laser line scanning thermography for surface breaking crack detection : modeling and experimental study

Crack detection in metallic samples at high surface temperature, hostile and hazardous environments, etc. is a challenging situation in any manufacturing industries. Most of the present NDE methods are suitable only for lower surface temperatures, especially at room temperature. In this situation, we need a fast and non-contact NDT method which can be applied even in high sample surface temperature. Laser thermography is one of the techniques having a high potential in non-contact inspection. As a preliminary investigation, in this article, we have studied the potentiality of laser line thermography in crack detection at room temperature. In laser line thermography, a continuous wave (CW) laser is used to generate a laser line, which in turn is used to scan the metal surface. The heat distribution over the sample surface is recorded by an infrared thermal (IR) camera. Two different approaches are reported in this work. Firstly, a stationary laser line source and its interaction with cracks; secondly, moving laser line source scanning over a surface with crack. When the distance between crack centre to laser line centre increases, crack detectability will decrease; and when laser power increases, crack detectability will increase. A dedicated image processing algorithm was developed to improve the detectability of the cracks. To understand the heat transfer phenomenon, a simplified 3D model for laser thermography was developed for the heat distribution during laser heating and was validated with experimental results. Defects were incorporated as a thermally thin resistive layer (TTRL) in numerical modeling, and the effect of TTRL in heat conduction is compared with experimental results.

Неразрушающий контроль композиционных материалов

Composite materials are widely used in a number of industrial sectors from aviation, space, to boat building, automotive, and sports goods. In recent years composite structures have seen a substantial increase of their use in the new generation of airplanes. The nondestructive testing and inspection of composite structures, both for manufacturing quality assurance and for in-service damage detection, has prompted the development and adaptation of a number of methods and techniques over the years. In this paper we review the various NDT methods for inspecting composites including water- and air-coupled ultrasound, bond testing, manual and automated tap testing, radiography, thermography, and shearography with emphasis given to techniques that demonstrated benefits to the practice of composite inspection.

Experiment Study of Ultrasonic Pulse Velocity Test of R/C Column Under Axial Load Variation

This study presents a simple NDT method with Ultrasonic Pulse Velocity (UPV) to detect repair of R/C columns by injection and grouting. In this paper, the technique applied is mainly based on the use of epoxy under pressure into the R/C column crack system for lightly damage, whereas grouting used for repair of medium and heavy damaged R/C columns. The specimen is initially charged to increase axial loads up to 0.1P0, 0.3P0 and 0.5P0. After repair, all specimens were retested with the same method. The test results show that the repair technique is in a good category with a pulse velocity value of 4.21km/s. Pulse velocity transmitter analysis provides conceptual support to increase column capacity through repair methods. Direct methods can be recommended for post-repair structural strength with high accuracy. This method is a potential candidate for future development, especially to predict the level of damage and building rehabilitation after an earthquake.

Durability Assessment of Concrete by using Electrical Resistivity & Rapid Chloride Permeability Technique

The durability of concrete is generally evaluated by many NDT technique, among the different NDT technique RCPT is one of the popular NDT method used by many researchers & practicing Engineers for evaluation of concrete durability. However the RCPT technique has some limitation on field test of concrete, considering the limitation of the RCPT technique a new technique has been intr oduced called Electrical resistivity technique is used for evaluation of concrete durability in both field & lab test. Durability of concrete is mainly depends on the properties of concrete microstructure i.e. pore size distribution, shape & connectivity of the microstructural pores in concrete. In general smaller pore size, with lesser connectivity results lower permeability & shows more durability, while concrete with porous microstructure having larger pore size distribution along with larger degree of interconnections results in higher permeability and shows poor durability. In this paper an experimental studies were conducted for evaluation of concrete durability on different types of concrete samples by using electrical resistivity & RCPT technique. From the experimental results it has been observed that concrete with lower level of Chloride permeability shows higher Electrical resistivity. Thus Electrical resistivity of concrete is directly influencing the durability of concrete.

Characteristic Curve and Its Use in Determining the Compressive Strength of Concrete by the Rebound Hammer Test.

During the construction of concrete structures, it is often useful to know compressive strength at an early age. This is an amount of strength required for the safe removal of formwork, also known as stripping strength. It is certainly helpful to determine this strength non-destructively, i.e., without any invasive steps that would damage the structure. Second only to the ultrasonic pulse velocity test, the rebound hammer test is the most common NDT method currently used for this purpose. However, estimating compressive strength using general regression models can often yield inaccurate results. The experiment results show that the compressive strength of any concrete can be estimated using one’s own newly created regression model. A traditionally constructed regression model can predict the strength value with 50% reliability, or when two-sided confidence bands are used, with 95% reliability. However, civil engineers usually work with the so-called characteristic value defined as a 5% quantile. Therefore, it appears suitable to adjust conventional methods in order to achieve a regression model with 95% one-sided reliability. This paper describes a simple construction of such a characteristic curve. The results show that the characteristic curve created for the concrete in question could be a useful tool even outside of practical applications.

Effect of Thermal Loading on Selected Parameters of Reinforced Concrete Obtained by Acoustic NDT Method

The paper presents the results of experiments carried out on test samples made from reinforced concrete. Within this experiment, concrete beams with steel reinforcement in the middle were made. The concrete samples were tested by a non-destructive acoustic Impact-echo method before and after high temperature loading (after cooling to room temperature). We focused on the dominant frequencies shift in the frequency spectra obtained by this method. The aim was to assess the ability of aforementioned acoustic method to detect the thermal damage of steel reinforced concrete.

Comparison of infrared thermography, ground-penetrating radar and ultrasonic pulse echo for detecting delaminations in concrete bridges

Buildings, bridges, roads, and other structures need to be regularly maintained if they are to last. In general, if a defect is detected early, the cost of its remediation is typically much lower than if the structure is allowed to degrade for months or years. A key means of locating hidden defects are non-destructive testing methods. This paper describes measurements that compare three non-destructive methods applied to a concrete bridge and a laboratory specimen with artificial defects to simulate cavities. Three methods (infrared thermography, ground-penetrating radar and ultrasonic pulse echo) were used to measure the depth and size of cavities in the concrete panel. Furthermore, the measurements were made using two different brands of radar and two different thermal imaging cameras from the same manufacturer. Lastly, the NDT methods were compared across general performance criteria in terms of accuracy, testing practicality, and costs.

Experimental Testing of Aramid Composite Applied in Ballistic Armour by Ultrasonic IR Thermography

Reference samples, in which artificial discontinuities (defects) are fabricated, are used to verify non-destructive testing procedures. Artificial discontinuities are known defects of reference samples and enable verification the feasibility of the verified NDT method for the identification of location and depth of discontinuities. Thermographic inspection of reference samples also helps to determine the required thermal input source parameters to test samples. This paper presents the results of experimental testing for ultrasonic IR thermography of defects in aramid composite laminate intended for light ballistic armour. Specimens of the aramid composite material included artificial defects and were inspected at various ultrasonic frequencies. Optical thermography and X-ray inspection were carried out on the same specimens, and their results were compared to those determined with ultrasonic IR thermography.

Development of NDT Methods for Control of Building and Bridge Structures in Bulgaria

Development of NDT Methods for Control of Building and Bridge Structures in Bulgaria

Shear failure characterization in masonry components made with different mortars based on combined NDT methods

In this paper, an experimental study conducted on Red Clay brick masonry “triplets” built with Cement and Lime-based mortars is presented. Monitoring of fracture is executed by Acoustic Emission (AE) and Digital Image Correlation (DIC). First, for a profound understanding of individual properties, small scale experiments were conducted for characterization of AE signatures of mortar and brick separately. Representative masonry triplet elements are tested in shear for investigation of the fracture mechanisms in relation to the properties of different mortars. Localization of the cracks as well as source identification is performed by means of AE parameter-based analysis. Their correlation with DIC, accurately showed the location of macro cracking and the developing of strain concentrations even before fracture. This is one of the first investigations where full field strain pattern from DIC are successfully correlated with AE indices in masonry. Numerical simulations were also performed for validation and prediction purposes.

Monitoring of Thermal Damage Evolution in Concrete Parts by Acoustic NDT Methods

The paper presents the results of the experimental work which was focused on the use of the Impact-echo method for testing of concrete specimens damaged by high-temperature. The test specimens were heated to 600 and 800 °C for sixty, one hundred twenty and three hundred minutes. After heating, the samples were continuously cooled to room temperature and tested by Impact-echo method.

Creep failure of a steam pipe girth weld and NDT strategy on creep damage

12Cr1MoV is a commonly used heat-resistant steel for the steam pipelines of subcritical power boilers in China. Usually, the girth weld joints are the weakest areas of the entire steam pipelines. In this work, a leakage failure of girth weld joint in a 12Cr1MoV steam pipe with about 10 years' service was analyzed. The crack is along the intercritical heat affected zone (ICHAZ) in the hoop direction, and the fracture completely duplicating the geometry of the fusion line. The microstructure had degraded seriously by carbides spheroidization. In the region of ICHAZ and FGHAZ (type IV zone), creep cavities were observed along the grain boundaries. These phenomena indicate the weld joint had suffered type IV creep cracking. The formation and accumulation of the cavities in type IV zone of the weld joint before cracking is a unique phenomenon of creep. Therefore, the proper NDT method and signal extraction with strong ability on cavities recognition should be the key points for detecting the creep damage in early stage. The sensitivity and selectivity of the signal are both important for the practical application on the creep inspection.

Current possibilities of the diagnosis of prestressing steel in structures

The field of diagnosis of structures has been experiencing a dynamic development in the last decades caused by the development and expansion of new NDT methods and instrumentation. At the same time, it is possible to observe changes in the focus of interest in this field, or more precisely, alternating waves of interest in specific types of diagnosis targeted at special types of structures. These waves of interest are always caused by a certain trend in the development of the society or building industry, and most often, by some major even in the field. In the last few years, particular attention has been paid to prestressed structures, especially to bridges, in connection with the recent accidents of bridges made from prestressed concrete in the Czech Republic and abroad. Considering the relatively large number of these bridges in the Czech Republic built in the second half of the 20th century, attention is paid to basic changes in the pre-construction condition surveys aimed at determining the condition and the remaining life of these structures. The paper focuses on the analysis of possibilities of assessing the condition of prestressing steel at the level of the present state of diagnosis of structures.

Shearography Technique on Inspection of Advanced Aircraft Composite Material

The A320 aft fixed fairing is an advanced composite structure fabricated from laminate carbon woven and combines with honeycomb core which is externally mounted on the flap track fairing as a wing part of Airbus aircraft. These flaps are movable control surfaces to widen up the surface of the wing in order to increase the lifting. This paper discussed on the inspection of A320 aft fixed fairing by using shearography NDT technique. Shearography technique reveals the stress-affected zone due to additional loading that can be realized by the laser speckle correlation on the inspected composite panel. This A320 aft fixed fairing is identified as a scrap composite panel which having different sizes and orientations of defect. The results showed that the changes of shearing direction in laser shearography technique are an effective means to reveal the defects propagation in the composite component. The shearing at Y-axes direction is able to detect the cracks at horizontal orientation while shearing at X-axis has successfully detects the cracks at vertical orientation. Therefore, shearography could be utilized as an alternative inspection for other NDT method for inspection of composite material.

Inspection of casting defects and grain boundary strengthening on stressed Al6061 specimen by NDT method and SEM micrographs

Non-destructive testing is one part of the function of quality control and is complementary to other long-established methods. By definition, non-destructive testing is the testing of materials, for surface or internal flaws or metallurgical condition, without interfering in any way with the integrity of the material or its suitability for service. The methods covered are Radiography, Magnetic Particle Crack Detection, Dye Penetrate Testing, Ultrasonic Flaw Detection, Eddy Current and Electro-Magnetic Testing. Here in this project work by using the radiography method of NDT testing is followed to identify the internal defects of the Al6061 cast specimen that was made by stir casting method. The aluminum cast structure involved to mono and multi-heat treated at about 450°C and 600°C in a muffle furnace and is compressed mechanically by using hydraulic press arrangements before the brief inspection through NDT testing. This technique is suitable for the detection of internal defects in ferrous and nonferrous metals and other materials. Furthermore, the denser the material greater will be the absorption. After the primary stage of inspection, most of the defects were identified by the NDT methods. In the second part of this project, SEM images can be taken for the compressed casting structure. The structural changes were successfully made on the cast specimen and the bond strength, as well as hardness were also increased. The comparison was made between the NDT inspected values and the SEM microstructure. It shows the clear representation of the grain structure and the bond strength.

Grease-like coupling agent based on metal ionization method for low-frequency ultrasonic NDT

Abstract In long-distance NDT based on ultrasonic guided waves with low-frequency excitation, the most commonly used industrial coupling agents are grease-like coupling agents. However, these agents show the poor performance in NDT, because they can cause more acoustic energy loss and lower acoustic transmissivity. In the study, to improve the acoustic transmission property of grease-like coupling agents, a new method was proposed to combine different metal ions like Li+, Na+ and Ca2+ with base grease, thus forming new grease-like coupling agents. By comparing with the ultrasonic transmitting property of the regular coupling agents, selects a premium ultrasonic grease-like coupling agent. In the experimental results, when low-frequency ultrasonic guided waves transmitted through the lithium-based coupling agent, except the slight delay of peak response time, pulse signals showed the higher energy transmission efficiency with the better pulse vibration waveforms in the iron medium than other oil-based coupling agents. The newly developed grease-like coupling agent can be easily prepared at a lower cost. Importantly, the new coupling agent can improve the energy transmission performance and greatly enhance the sensitivity of ultrasonic flaw detection.