Non-destructive Experimental Technique Research Articles

Non-destructive experimental technique to determine ball contact load in rolling machine elements

Rolling machine elements, such as ball bearings, ball screws, or guiding systems are commonly used in diverse industrial applications. These components typically assume uniform load distribution among the balls or rely on analytical expressions. However, experimental load distribution measurement remains a challenge. This research work proposes a non-destructive experimental technique designed to determine ball contact load. The method uses painted surfaces to visualize the contact area under each rolling element, combined with an analytical formulation that modifies Hertz’s original contact equations to account for the influence of the painted layer thickness. Analytical results are compared with experimental tests on flat and curved surfaces. The results show a good agreement between the proposed painted surface formulation and measured contact areas.

Microscopic moisture localisation in unsaturated materials using nuclear magnetic resonance relaxometry

Due to the detrimental effects of moisture in the built environment, there is a continuous interest in non-destructive experimental techniques that quantify and/or localise moisture in materials. Most existing experimental techniques, however, typically focus on macroscopic moisture contents in samples rather than the microscopic distribution of water in the individual pores of building materials. For the latter, a popular method such as X-ray computed tomography is not readily applicable, due to the gap between its spatial resolution limit and the typical pore sizes of building materials. Nuclear magnetic resonance (NMR) relaxometry is capable of measuring water in pores of both the nanometer and micrometer scale and is therefore an interesting possibility. While most NMR research focusses on water-saturated materials or overall moisture contents, this study determines the size distributions of the water islands in unsaturated materials with NMR, and compares results to X-ray computed tomography (XCT) images and pore network model (PNM) simulations. Results on unsaturated materials show that NMR focusses on the biggest water islands (i.e. in capillary filled pores) and disregards the hydrogen nuclei in smaller water islands (i.e. stored in pore corners). NMR relaxometry is therefore only adept at providing very rough estimates of the size of water-filled pores, especially since post-processing of the NMR experiments to obtain these water island size distributions involves a lot of uncertainty.

Moisture localisation in unsaturated materials using nuclear magnetic resonance experiments, X-ray computed tomography and pore network modeling

Due to the detrimental effects of moisture in the built environment, there is continuous interest in non-destructive experimental techniques that localize and/or quantify moisture in materials. To this aim, nuclear magnetic resonance (NMR) experiments, X-ray computed tomography (XCT) and pore network modelling (PNM) are heavily researched. Since these techniques are all based on different physical principles and assumptions, comparing their results is not only necessary, but can provide valuable insights as well. Since most research, centered around these three approaches, solely focuses on water-saturated materials, in this study, these approaches are used to determine the size distributions of the water islands in unsaturated materials. By comparing the results of all three methods, it can be concluded that NMR mainly focuses on the biggest water islands/columns (i.e. large pore corners and filled pores) while the other techniques are capable of representing all water islands. PNM and XCT imaging provide similar results with the exception that PNM slightly overestimates both size as well as quantity of the water islands trapped in pore corners. Nevertheless, due to PNM being by far the fastest approach, it remains a valuable first estimation of the distribution of moisture in unsaturated materials.

Fractal Characterization of Brass Corrosion in Cavitation Field in Seawater

Cavitation is a physical process that produces complex effects on the machines and components working in conditions where it acts. One effect is the materials-mass loss by corrosion–erosion when components are introduced into fluids under cavitation. The analysis of the damages produced by cavitation is generally performed by using different destructive and non-destructive experimental techniques. Most studies on materials’ behavior in cavitation refer to the erosion–corrosion mechanism, and very few investigate the fissure propagation by fractal methods. None have investigated the fractal characteristics of the sample surface after erosion–corrosion or the multifractal characteristics of materials’ mass variation in time in a cavitation field. Therefore, this research proposes a computational approach to determine the pattern of materials’ damages produced by ultrasound cavitation. The studied material is a brass, introduced in seawater. Fractal and multifractal techniques are applied to the series of the absolute mass loss per surface and the sample’s micrography after corrosion. Such an approach has not been utilized for such a material in similar experimental conditions. This study emphasizes that the box dimension of the series of the absolute mass loss per surface is close to one, and its behaviour is close to a non-/monofractal. It is demonstrated that the material’s surface corrosion is not uniform, and its multifractal character is highlighted by the f(α)− spectrum and the multifractal dimensions, which have the following values: the capacity dimension = 1.5969, the information dimension = 1.49836, and the correlation dimension = 1.4670.

Photoreflectance system based on vacuum ultraviolet laser at 177.3 nm

Photoreflectance (PR) spectroscopy is a powerful and non-destructive experimental technique to explore interband transitions of semiconductors. In most PR systems, the photon energy of the pumping beam is usually chosen to be higher than the bandgap energy of the sample. To the best of our knowledge, the highest energy of pumping laser in reported PR systems is 5.08 eV (244 nm), not yet in the vacuum ultraviolet (VUV) region. In this work, we report the design and construction of a PR system pumped by VUV laser of 7.0 eV (177.3 nm). At the same time, dual-modulated technique is applied and a dual channel lock-in-amplifier is integrated into the system for efficient PR measurement. The system’s performance is verified by the PR spectroscopy measurement of well-studied semiconductors, which testifies its ability to probe critical-point energies of the electronic band in semiconductors from ultraviolet to near-infrared spectral region.

Single-Phase Precursors for the Preparation of Spinel Ferrites via Oxalate Route: the Study of Cobalt Ferrite Synthesis.

This work explores the benefits of single-phase oxalate precursors for the preparation of spinel ferrites by thermal decomposition. A direct comparison between the genuine oxalate solid solution and the physical mixture of simple oxalates is presented using the case study of cobalt ferrite preparation. The mixing of metal cations within a single oxalate structure could be verified prior to its thermal decomposition by several non-destructive experimental techniques, namely Mössbauer spectroscopy, X-ray powder diffraction (XRD) and energy-dispersive X-ray spectroscopy. In situ XRD experiments were conducted to compare the decomposition processes of the solid solution and the physical mixture. Additionally, the decomposition products of the FeCo oxalate solid solution were studied ex situ by means of N2 adsorption, Mössbauer spectroscopy and XRD. The results obtained for different reaction temperatures demonstrate the possibilities to easily control the physical properties of the prepared oxides.

Analytical approach of colour and elemental composition in gold metallic objects from the Quimbaya culture: A case study in Antioquia, Colombia

Colour has been an outstanding feature in the Quimbaya culture. This attribute was related to its gold artifacts and alloys. However, few studies have provided insight into the relationship between gold contents and colour in these pre-Hispanic artifacts. As an initial approach to evaluate these characteristics, in this paper the elemental composition and surface colouration of ten pre-Hispanic goldwork samples found in Antioquia-Colombia, belonging to the early and late Quimbaya culture, were studied. Thisstudy was done using portable and non-destructive experimental techniques such as energy dispersive X-ray fluorescence spectroscopy - EDXRF and UV–Vis fibre optic spectrophotometry. The results indicated that mostpieces contained the elements Au, Ag and Cu, with the highest concentration being Cu (∼18% – 40%) in seven of the samples tested. At first glance, colour changes due to elemental concentrations are noticeable in all objects. To verify those changes, a colourimetric analysis was performed through optical reflectance spectrum analysis, using a new empirical model written in MATLAB. The software allows the processing of all reflectance spectra and estimates the colourimetric parameters (a *, b *, C *, L *, h *). We found that the spectra are sensitive to changes in elemental concentrations other than gold and copper (Ag and Cu). According to the colourimetric parameters a* and b*, two groups of objects associated with early and late temporality are differentiated. The results reveal a correlation between the hue (h*) and the Au and Cu concentrations.

Space Charge Redistribution in Epoxy Mold Compounds of High-Voltage ICs at Dry and Wet Conditions: Theory and Experiment

Space charge profile plays an important role in defining the charge transport and breakdown field of an insulator. Non-destructive experimental techniques (e.g., PEA measurement) have recently been used to track in-situ the time-evolution of space charge profiles within complex insulators, such as epoxy mold compounds. Unfortunately, the published results are often inconsistent (both positive and negative charge build-up have been reported), and the discrepancy remains unexplained. In this paper, we (i) derive a physics-based compact analytical model of homocharge injection, (ii) explain the time-and voltage-dependent redistribution of homo- and heterocharge, (iii) investigate experimentally and explain theoretically the importance of moisture ingress regarding space charge redistribution, and finally, (iv) summarize strategies to suppress space-charge related instability in modern ICs encapsulated by epoxy mold compounds.

Post-Breakage Vibration Frequency Analysis of In-Service Pedestrian Laminated Glass Modular Units

The vibration performance of pedestrian structures has attracted the attention of several studies, especially with respect to unfavourable operational conditions or possible damage scenarios. Specific vibration comfort levels must be commonly satisfied in addition to basic safety requirements, depending on the class of use, the structural typology and the materials involved. Careful consideration could be thus needed at the design stage (in terms of serviceability and ultimate limit state requirements), but also during the service life of a given pedestrian system. As for structural health monitoring purposes, early damage detection and maintenance interventions on constructed facilities, vibration frequency estimates are also known to represent a preliminary but rather important diagnostic parameter. In this paper, the attention is focused on the post-breakage vibration analysis of in-service triple laminated glass (LG) modular units that are part of a case-study indoor walkway in Italy. On-site non-destructive experimental methods and dynamic identification techniques are used for the vibration performance assessment of a partially cracked LG panel (LGF), compared to an uncracked modular unit (LGU). Equivalent material properties are derived to account for the fractured glass layer, and compared with literature data for post-breakage calculations. The derivation of experimental dynamic parameters for the post-breakage mechanical characterization of the structural system is supported by finite element (FE) numerical models and parametric frequency analyses.

Microscale Physical and Mechanical Analyses of Distemper Paint: A Case Study of Eidsborg Stave Church, Norway

ABSTRACT This study focuses on the use of micro-sensitive methods – nanoindentation, dynamic water vapour sorption, and X-ray microtomography – to examine the physical properties of small volumes of artists’ materials. The novel methodology proposed in this paper was tested on laboratory-prepared chalk-based ground samples and subsequently applied to distemper paint samples taken from the polychrome walls of Eidsborg stave church. This article discusses key parameters that can be used to inform macro-sized mock-ups mimicking physical and mechanical behaviour of artistic materials, and highlights limitations of such an approach for highly heterogeneous paint systems. Dynamic water vapour sorption measurements allowed determination of the pigment volume concentration (PVC) of distemper paint from Eidsborg stave church as 95%. To the authors’ knowledge, this represents the first assessment of PVC for historic distemper paint using a non-destructive experimental technique, which can be extended to other hygroscopic samples of known composition.

Identification of magnetic induced strain of electrical steels using non-destructive acceleration measurement and inverse vibration modeling

Magnetic induced strain is an important source of vibration in electromagnetic components and electrical machines. This magneto-mechanical behavior is identified using a non-destructive experimental technique that consists in measuring in a Single Sheet Tester the time dependent acceleration at the free end of a fixed-free magnetic sheet and its corresponding magnetic field and induction signals. The determination of this property in the longitudinal direction is investigated using an inverse application of the longitudinal vibration equation. The strain dependence on the exciting frequency as function of the resonance frequency is also evaluated. The apparent strain that includes the inertia effect is distinguished from the magnetic-induced strain. Both strains are identified and analyzed for different frequencies lower and higher than the sample’s natural frequency. We also investigated the effect of excitation’s harmonics on the mechanical response.

Curvature analysis of single layer graphene on the basis of extreme low-frequency Raman spectroscopy

Single layer graphene (SLG) sheets offer exciting optical and electronic properties, as well as excellent mechanical performance, which are desirable for countless potential applications in ultrathin optical, electronic, and mechanical devices. Typically, the mechanical properties of SLG are extrapolated from few layer graphene (FLG) systems in most existing experimental studies, despite the fact that the environmental mechanical response of SLG is quite different from FLG. Raman spectroscopy is one of the most versatile and nondestructive experimental techniques to probe graphene samples. Here, we provide direct experimental evidence for the vibrational behavior of SLG and its response to high pressure conditions (0–10 GPa) via Raman spectroscopy including the extreme low-frequency Raman region (5–250 cm–1). Artificial introduction of the curvature of the SLG sheets causes van Hove singularities within the range of Fermi energies (EF). The radius of curvature ρ can be predicted via a comparison of the shear mode and the breathing mode of SLG with the squash mode and the radial breathing mode of single wall carbon nanotubes (SWNTs). Furthermore, an additional polarization analysis further confirms similar low frequency modes of SLG and SWNTs under pressure. This direct investigation of SLG mechanical properties improves the quality of the available mechanical data, which is required for the design of new graphene-based nanocomposites and the development of electronic or mechatronic devices.

Contactless safety evaluation of damaged structures through energetic criteria

Summary The reinforced concrete structures need to be monitored to ensure their structural integrity, but sometimes those measurements are very local, and the instrument is complex to locate physically in the structure and may interfere on it. Digital Image Correlation is a noncontact and nondestructive experimental technique capable to measure the displacement field in a big region of a structure with a great accuracy. This allows extracting valuable information from the fracture processes of reinforced concrete structures, critical for the evaluation of the structural integrity. The measurement of the energy dissipated by the structure is essential for the identification of the strength mechanisms that are failing in the structure and to identify a proper repair. Also, using fracture mechanics, other valuable information are extracted from the fracture processes of the reinforced concrete beam, such as the Modes I and II fracture energy released at each loading step, which is essential to evaluate the elastic energy that the structure can accumulate before collapse. The examples enable to anticipate the importance of Digital Image Correlation for future large scale studies of fracture in concrete and other materials related to construction.

Evolution of the pore structure during the early stages of the alkali-activation reaction: an in situ small-angle neutron scattering investigation

The long-term durability of cement-based materials is influenced by the pore structure and associated permeability at the sub-micrometre length scale. With the emergence of new types of sustainable cements in recent decades, there is a pressing need to be able to predict the durability of these new materials, and therefore nondestructive experimental techniques capable of characterizing the evolution of the pore structure are increasingly crucial for investigating cement durability. Here, small-angle neutron scattering is used to analyze the evolution of the pore structure in alkali-activated materials over the initial 24 h of reaction in order to assess the characteristic pore sizes that emerge during these short time scales. By using a unified fitting approach for data modeling, information on the pore size and surface roughness is obtained for a variety of precursor chemistries and morphologies (metakaolin- and slag-based pastes). Furthermore, the impact of activator chemistry is elucidated via the analysis of pastes synthesized using hydroxide- and silicate-based activators. It is found that the main aspect influencing the size of pores that are accessible using small-angle neutron scattering analysis (approximately 10–500 Å in diameter) is the availability of free silica in the activating solution, which leads to a more refined pore structure with smaller average pore size. Moreover, as the reaction progresses the gel pores visible using this scattering technique are seen to increase in size.

Influence of some Oxide Coating Layers on the Mechanical Properties of Steel Plates

The paper presents a vibroacoustic method to determining the stiffness of coated steel with various materials such as metal oxides, metallic paints, polymers etc and Young's modulus for coating materials. The method consists in measuring the dynamic response of the steel in the form of a rectangular bar subjected to external impulse. One of the latest non-destructive experimental techniques in this field is based on the analysis of vibrating signal response recorded with a condenser microphone. A Fast Fourier Transform algorithm is used for processing the sampled signals. Knowing the mechanical properties of steel plates prior to coating with metal oxides, and determining the same properties after coating, can be obtained the mechanical properties of metal oxides and their influence on the properties of the ensemble.

Characterization of Material Damage by Ultrasonic Immersion Test

We present an innovative non-destructive experimental technique for a quantitative determination of the damage level in structural components. In particular, we study the propagation of ultrasonic waves in an isotropic material specimen before and after a mechanical fatigue incremental test. To this aim, we use an innovative goniometric device for ultrasonic immersion tests, designed and built for the mechanical characterization of anisotropic materials. In the first test, performed in absence of damage, we characterize the mechanical behavior of the isotropic material by the measure of time of flight (TOF) of ultrasonic waves, and then by determining the so-called natural velocities. In the next ultrasonic tests, performed after each fatigue test, we determine the response of the damaged material by measuring again the velocity of ultrasonic waves: the comparison between these velocities and the natural velocities allows for the evaluation of the level of damage in the material. Moreover, through the goniometric ultrasonic immersion device it is possible to relate the damage to the stress-induced anisotropyacquired by the specimen, which we characterize by identifying the acoustic axes and the dependence of the velocity of the ultrasonic waves on the direction of propagation.

Surface Plasmon Resonance Ellipsometry Based Biosensor for the Investigation of Biomolecular Interactions

The method of ellipsometry, particularly spectroscopic ellipsometry, is a very sensitive, non-destructive experimental technique of thin film characterisation. The recently proposed method of Surface Plasmon Resonance Ellipsometry (SPRE) combines the advantages of spectroscopic ellipsometry and the Kretschmann type SPR geometry of total internal reflection. We describe aspects of this experimental approach by focusing on some particular possibilities for different sensing applications in liquid media, as well as for organic molecular thin film characterization. The modeling reveals detection limit of changes in the bulk refractive index of Δnb = 1.5 × 10-6 which represents an instrumental potential for the concentration limit of an analyte at several pmol/liter in a solution. In each part methodological importance and its specificity for studying molecular interactions is stressed. The typical time of the measurement, which is approx. 2 s, enables the molecular adsorption processes or biomolecular reactions at the interface to be monitored in a real time. According to the experiments carried out in a static SPR cell with the aptamer immobilized layer a concentration of less than 0.1 nmol/liter of thrombin in a buffer solution was observable following the typical saturation shape

CO2 and Temperature Effects on the Asphaltene Phase Envelope As Determined by a Quartz Crystal Resonator

Knowledge of the asphaltene phase envelope (APE) is crucial for oil companies, especially when enhanced oil recovery is applied. An innovative quartz crystal resonator (QCR) technique was employed to assess the phase behavior of asphaltene under reservoir conditions. The effect of CO2 injection coupled to temperature changes on the APE of a recombined oil with a very low asphaltene content (0.235% w/w of C7 asphaltene in dead oil) are reported. It has been shown that QCR is an appropriate and highly sensitive nondestructive experimental technique for detecting asphaltene flocculation. Pressure onsets were found to be dependent on the depressurization rate.

Evaluation of Prestress Force on Bonded Tendons Using Practical Formula

This work introduces a non-destructive experimental technique to evaluate the existing prestress level on bonded tendons embedded in a post-tensioned concrete structure. By measuring the longitudinal stress wave velocity on the strands, the applied stress level can be evaluated using an experimental formula. The experimental relation between the applied stress levels and the stress wave velocity is derived from various impact-echo test results for a set of prestressed concrete beam specimens with different tensile stress levels. The experimental results reveal that the longitudinal stress wave velocity of the bonded strands increases nonlinearly as the applied tensile stress level increases. To investigate the field applicability and feasibility of the approach, longitudinal impact-echo tests are conducted for two prestressed bonded tendons embedded in a nuclear reactor containment building. This reveals that the proposed approach is feasible and applicable for the unique identification of the existing prestress levels on the individual strands embedded in a real post-tensioned concrete structure.

Measurement of Young’s Modulus and Shear Modulus of Some Structures Welded Using Flux Cored Wire by Vibration Tests

The aim of this work was to determine by vibration tests the longitudinal elastic modulus and shear modulus of welded joints by flux cored arc welding. These two material properties are characteristic elastic constants of tensile stress respectively torsion stress and can be determined by several non-destructive methods. One of the latest non-destructive experimental techniques in this field is based on the analysis of the vibratory signal response from the welded sample. An algorithm based on Pronys series method is used for processing the acquired signal due to sample response of free vibrations. By the means of Finite Element Method (FEM), the natural frequencies and modes shapes of the same specimen of carbon steel were determined. These results help to interpret experimental measurements and the vibration modes identification, and Youngs modulus and shear modulus determination.