Optical Testing Methods Research Articles

Multimodal Non-Destructive In Situ Observation of Crystallinity Changes in High-Density Polyethylene Samples with Relation to Optical Parameters during Tensile Deformation

Abstract: Many non-destructive optical testing methods are currently used for material research, providing various information about material parameters. At RECENDT, a multimodal experimental setup has been designed that combines terahertz (THz) spectroscopy, optical coherence tomography (OCT), infrared (IR), and Raman spectroscopy with a tensile test stage. This setup aims to gather material information such as crystallinity and optical parameters of high-density polyethylene (HDPE) during a tensile test. The setup compares common IR and Raman spectroscopy and the less common optical methods THz and OCT. Complementarity is achieved through different frequency ranges and measurement approaches, resulting in different measured optical material parameters and depths. During tensile testing, HDPE samples with varying crystallinity were analysed, and the determined optical parameters such as refractive index, birefringence, scattering coefficient of decay, and penetration depth can be correlated with the change in crystallinity. These findings demonstrate that the optical methods and their outcomes can be interconnected. With further optimization of the experimental setup, it would be possible to observe the alignment of fibres in fibre composite panels and the stress distribution of polymers effectively. This opens interesting possibilities for polymer characterization in the future, including quality control during moulding processes and material testing.

Improved Foucault method with double-shoot shadow grams in optical shop testing.

The lack of rapid, effective, and quantitative testing methods in the initial stages of optical processing has been identified as a significant challenge. In response, an innovative approach has been developed to enhance the Foucault knife-edge test method, integrating digital image processing and spatial geometry algorithms. This has resulted in the creation of a convenient and rapid optical testing method, which has been successfully implemented in practice. The method requires the collection of only two knife-edge shadow grams, which are then subjected to calculation. This enables the theoretical results of the knife-edge shadow gram at the focal point, and the reference results of the wavefront surface processing error of the mirror to be measured can be obtained. The method can be well applied to the testing work of optical workshops and provides a guiding solution with better performance for optical testing than the traditional knife-edge testing method.

Multi-sample joint localization method for intrusion sources around underground pipelines based on cross-correlation convolutional neural networks

Improving the safety monitoring of underground pipelines is crucial for maintaining the structural integrity of critical infrastructure systems. This study introduces an innovative multi-sample joint localization method (MSJLM) based on cross-correlation convolutional neural networks (CC-CNNs) to identify intrusion sources in the vicinity of underground pipelines. Traditional approaches to detecting and locating pipeline intrusions often rely on a solitary sensor monitoring point, making them susceptible to errors and limitations. Presently, widely used distributed optical fiber testing methods tend to yield imprecise localization. In contrast, the MSJLM proposed in this study harnesses data from multiple samples effectively and combines them via correlation analyses to enhance precision and reliability. The CC-CNN framework used to process the collected data is demonstrated to be highly effective in extracting spatial features and recognizing patterns.

MALDI-TOF MS combined with AUC method for tigecycline susceptibility testing in Escherichia coli.

The wide spread of tet(X4) gene orthologues in the environment, food, poultry and humans is causing serious tigecycline resistance. Consequently, developing a fast and universal method to detect tigecycline resistance has become increasingly important. During 2019-2022, 116 Escherichia coli isolates were obtained from nine provinces in China. All isolates were tested for their susceptibility to antimicrobial agents by the microdilution broth method and for the tet(X4) gene by PCR. Ten tet(X4)-positive E. coli isolates were used to confirm certain conditions, including the optimal incubation time, the optimal concentration of tigecycline, and the cut-off of the relative growth (RG) value. The optimal time and concentration of tigecycline for separation of susceptible and resistant isolates was 2 h and 4 mg/L, and the RG cut-off value was 0.4. We validated whether the experiment was feasible using 116 isolates of E. coli. The method yielded a susceptibility of 94.9% (95% CI: 81.4%-99.1%) and a specificity of 96.1% (95% CI: 88.3%-99.0%). This research has shown that this optical antimicrobial susceptibility testing method can rapidly differentiate between susceptible and resistant phenotypes in isolates of E. coli. In the same range as the current gold-standard methods, the clinical turnaround time is reduced from 48 h to 2.5 h. The above results suggest that the method has splendid specificity and operationality.

SIMULATION OF THERMAL COMPENSATION OF OPTICAL TESTING DATA OF COMPOSITE STRUCTURES BY AN EXTERNAL FIBER-OPTIC TEMPERATURE SENSOR

This article describes the theoretical aspects of thermal compensation of data from optical non-destructive testing of deformation of structures made of polymer composite materials using fiber-optic sensors based on fiber Bragg gratings. It is shown that at the stage of bench testing of composite structures, the method of thermal compensation using an external temperature sensor can be successfully applied. Linear and quadratic mathematical models of thermal compensation are analyzed and generalized. It has been established that with the comparative simplicity of the implementation of this method of thermal compensation, the error in determining the deformation is also provided at the level of the error of the interrogator. However, for online testing of composite structures during operation, the use of this method is difficult, due to the fact that the placement of an external temperature sensor is not always possible. The proposed method and the corresponding models can be applied in practice to develop methods for optical testing of samples and structures made of polymer composite materials during bench and other tests, taking into account thermal compensation.

Accurate cavity volume testing based on micropressure differential gas inflation and deflation

For cavity volume testing, conventional optical or acoustic direct test methods are not only limited in terms of measurement efficiency, but also have difficulty avoiding errors due to complex cavity structures. In this paper, we present a cavity volume test based on micropressure differential gas inflation and deflation. The principle of the method is to charge and deflate the test cavity and obtain a mapping between the microbe difference and the inflating flow rate. Variability curves of the pressure difference inside and outside the cavity are measured during the deflating process and the cavity volume is calculated using parameters such as the intake flow rate and differential pressure. The heat and mass transfer equations are formulated for the gas in the cavity under inflation and deflation conditions. Numerical simulations of the variability of the gas state parameters and their impact factors are performed to verify the feasibility of the volumetric measurements. An experimental setup for volume measurements is constructed and a cockpit is used as an application object for volume measurement experiments under different micropressure differential inflation and deflation conditions. It shown that, as a complement to geometrical physical measurements, this method can better characterize the gas volume of the cavity.

Study on the Weak Interlayer Identification Method Based on Borehole Photo-Acoustic Combined Measurement: Application to a Landslide Case Study

A weak interlayer is the key factor in controlling slope stability. It is of great significance to effectively identify the weak interlayer in the study of spatial and temporal distribution law and the internal structure characteristics of a landslide. Considering the limitations of traditional optical imaging and wave speed test methods, this paper presents a weak interlayer identification method based on borehole photo-acoustic combination measurement. By using the combination of optical imaging and acoustic wave scanning, the multi-source data collection of borehole rock wall and borehole surrounding rock is realized, which effectively captures the comprehensive response characteristics of the weak interlayer. This paper first constructs a multi-source data acquisition technology based on the borehole photo-acoustic combination measurement to realize the visualization of the image information and acoustic data of the target area on the borehole rock wall. Subsequently, the optical image features and the acoustic response characteristics of the weak interlayer are clarified based on the optical image and the acoustic scanning data. The hole wall texture characteristic response function, hole wall integrity characteristic response function, hole wall acoustic characteristic response function and hole wall contour characteristic response function are constructed. Finally, the landslide weak interlayer identification method considering the texture characteristics, complete characteristics, acoustic response characteristics and contour characteristics of the borehole rock wall is proposed, which effectively distinguishes the types of rock mass structural surface and realizes the automatic identification of the weak interlayer. Combined with the case analysis, the correctness and reliability of the present method are verified. The results show that the method can identify the weak interlayer and provide scientific basis for landslide management, which can provide a feasible and effective new way to identify the landslide weak interlayer in practical engineering, with a good application prospect and promotion value.

Fluorescence signatures of SARS-CoV-2 spike S1 proteins and a human ACE-2: excitation-emission maps and fluorescence lifetimes.

.Significance: Fast and reliable detection of infectious SARS-CoV-2 virus loads is an important issue. Fluorescence spectroscopy is a sensitive tool to do so in clean environments. This presumes a comprehensive knowledge of fluorescence data.Aim: We aim at providing fully featured information on wavelength and time-dependent data of the fluorescence of the SARS-CoV-2 spike protein S1 subunit, its receptor-binding domain (RBD), and the human angiotensin-converting enzyme 2, especially with respect to possible optical detection schemes.Approach: Spectrally resolved excitation-emission maps of the involved proteins and measurements of fluorescence lifetimes were recorded for excitations from 220 to 295 nm. The fluorescence decay times were extracted by using a biexponential kinetic approach. The binding process in the SARS-CoV-2 RBD was likewise examined for spectroscopic changes.Results: Distinct spectral features for each protein are pointed out in relevant spectra extracted from the excitation-emission maps. We also identify minor spectroscopic changes under the binding process. The decay times in the biexponential model are found to be and .Conclusions: Specific material data serve as an important background information for the design of optical detection and testing methods for SARS-CoV-2 loaded media.

Evaluation of wavefront aberrations induced by overlay errors in stitching computer-generated holograms

The emergence of large-aperture telescopes has fueled the need for testing and assisted alignment of large-scale optical systems. Computer-generated holograms (CGHs) have proven to be a useful method for aspheric optical testing and assisted alignment, and large-sized CGHs are required for large-scale aspherical systems. However, the maximum size of CGH is generally in the range of 6 to 9 inches owing to its current lithography capability. Stitching technology is a promising method for realizing larger-sized CGHs. As a proof of concept, a CGH with an aperture of 80 mm is fabricated using multistep lithography to investigate the overlay errors in stitching. Theoretical derivations reveal that additional tip/tilt aberrations are introduced owing to the overlay errors, which commonly couple with aberrations from adjustment errors. Therefore, to budget the effects of overlay errors, an evaluation method is proposed in this study. The evaluation results guide the separation and compensation of coupling aberrations in measurement. It is verified that the accuracy of a stitching CGH is considerably improved from 0.156λ to 0.017λ in terms of RMS after compensation. The findings obtained in this study during the development of stitching method and error evaluation are expected to promote the technology development and improvement of testing accuracy in stitching CGHs.

Energy Direction in Ultrasonic Impregnation of Continuous Fiber-Reinforced Thermoplastics

As a new and innovative processing method for fabrication for fiber-reinforced thermoplastic composites (CFRTs), the feasibility of ultrasonic welding technology was proven in several studies. This method offers potential for the direct manufacturing of CFRT–metal structures via embedded pin structures. Despite the previous studies, a deeper understanding of the process of energy input and whether fibers work as energy directors and consequently can, in combination with chosen processing parameters, influence the consolidation quality of the CFRTs, is still unknown. Consequently, the aim of this work is to establish a deeper process understanding of the ultrasonic direct impregnation of fiber-reinforced thermoplastics with an emphasis on the fiber’s function as energy directors. Based on the generated insights, a better assessment of the feasibility of direct, hybrid part manufacturing is possible. The produced samples were primarily evaluated by optical and mechanical test methods. It is demonstrated that with higher welding time and amplitude, a better consolidation quality can be achieved and that independent of the process parameters chosen in this study, no significant fiber breakage occurs. This is interpreted as a sign of a gentle impregnation process. Furthermore, based on the examination of single roving and 5-layer set-ups, it is shown that the glass fibers function as energy directors and can influence the transformation of sonic energy into thermal energy. In comparison to industrially available CFRT material, the mechanical properties are weaker, but materials and processes offer potential for significant improvement. Based on these findings, proposals for a direct impregnation and joining process are made.

Методи діагностування дефектів деталей авіаційних двигунів з композиційних матеріалів

The key priority in improving the technical and economic performance of gas turbine engines lays in the use of new composite materials. The use of composites in the components of critical load-carrying structures operating under static and dynamic loads during long service lives determines the need to predict the component lives. Also, in order to increase the safety of engine operation and improve the parts manufacturing process, timely defect detection in such structures is of great importance. This article is devoted to the detection of the composite parts defects and damages that occur at different stages of manufacturing and operation. The aim is to investigate the existing methods of non-destructive testing of composite materials, describe their functional concept, and determine the field of their application. The article considers acoustic, thermal, optical, and radiation testing methods. Among the acoustic methods, the phased array method is selected as the most informative and multipurpose. The acoustic emission method is also selected; it will allow real-time monitoring of defect growth during testing. Out of thermal methods, the vibrothermography method was selected as the most advanced among the thermographic sub-methods. It allows using the phenomenon of local defect resonance and thus ensures effective defect detection. Shearography is selected for investigation out of optical methods. The special aspects of the use of X-ray methods are considered through the example of X-ray computed tomography. It is concluded that the approach combining several methods can significantly increase the efficiency of defect detecting and help to assess their criticality. Active thermal testing is well suited for fast scanning of large-sized parts and searching for areas of defect accumulation. In the following, local methods, such as impedance, vibrothermography, or one of the ultrasonic, should be used. To measure deformations under static load, it is a good practice to use shearography. To identify progressive defects under static load, it makes sense to use the acoustic emission method.

Measuring large amplitude surface figure error using coordinate metrology

Advances in optical testing are as important as advances in fabrication because one can make only what one can measure. A high-precision metrology capability is utilized to close the gap between interferometric testing and lower precision metrology, laser radar, or contact-probe-based coordinate measuring machines (CMM) to accurately measure surfaces with large form error. This nearly universal optical testing method employs a precision CMM equipped with a non-contact, confocal probe. This technique was developed to characterize and align a broad spectrum of optical surfaces including ones with high slopes that are nearly impossible to measure using traditional interferometric testing without custom-made optics. Optical components covering a wide range of prescriptions, such as large convex conics, high-sloped aspherics, grazing-incidence x-ray optics, and highly deformed flats, were successfully measured. The resulting data were processed using custom-developed routines to determine the optic’s alignment, the departure from design surface, and the as-built prescription parameters. This information was used to verify and guide the development and fabrication of novel optics.

Non-propagation fast phase diverse phase retrieval for wavefront measurement with generalized FFT-based basis function.

Phase retrieval is an attractive optical testing method with a simple experimental arrangement. The sampling grids wave propagation computation based on the FFT operations is usually involved in each iterative process for the classical phase retrieval model. In this paper, a novel non-propagation optimization phase retrieval technique with the FFT-based basis function is proposed to accelerate wavefront measurement. The sampling grids wave diffraction propagation computation is converted to matrix-vector products that have small dimensions to reduce the computational burden. The diffraction basis function based on generalized numerical orthogonal polynomial and two-step Fresnel propagation is deduced, which is suitable for the generally shaped pupil. This paper provides a universal non-propagation framework to accelerate phase retrieval which is applicable to the arbitrarily shaped wavefront measurement.

Investigation into the Reciprocating Sealing Performance Based on an Optical Test Method

Reciprocating seals are essential elements for hydraulic cylinders. The status of the contact area between the seal and the counterpart directly determines the sealing performance. An optical test rig for the O-ring seal was constructed in this study to investigate the tribological characteristics among the contacting zone, where the cylinder was changed to be transparent and a microscope is employed to observe and record the sealing status. A numerical method coupling finite element analysis (FEA) and the mixed lubrication procedure is implemented for the theoretical analysis. A comparison between the simulation and the experiment for the sealing width, friction force, and leakage was conducted. During the reciprocating motion, it was found that the oil film thickness adhering onto the cylinder’s inner wall was not even along the axial direction and that the leakage oil would be accumulated at the stroke-end position because of the seal’s scraping effect. The topographic indicators for the contact mechanisms are discussed, and the results demonstrated that the implementation of the mean peak width (Rsm) for the asperity radius could obtain more reasonable results. The performance of the O-ring seal at different velocities was theoretically and experimentally investigated. With an increase in velocity, the leakage rate increased and the friction force decreased. The simulation results are consistent with the experimental results both in the overall trend and in the order of magnitude.

Experimental Study on the Relationship between Compression Stability and Deformation Localization of Viscous/Brittle Rock‐Like Materials

Rock‐like materials often exhibit irregular failure deformation under long‐term service conditions, and the deformation and failure of asphalt and concrete materials is a serious problem that leads to subgrade failure. In this study, two different viscous/brittle rock‐like materials were prepared by the in situ loading and optical speckle synchronous monitoring test method, and the evolution characteristics of the deformation field were studied during compression. The formation process of the compression deformation localization of rock‐like materials and their relationship with stability were analyzed. A quantitative description of the compression deformation stage and localization characteristics of the viscous/brittle rock‐like materials is presented. The results can be summarized as follows. At the initial stage of compression, the deformation localization zone of viscous/brittle rock‐like materials begins to expand from the middle area to the surrounding area. Preliminary results of the deformation localization of the linear elastic deformation stage were obtained. The failure cloud image is completely formed at the peak, which is consistent with the failure physical map. The deformation process of compression can be quantitatively described using the deformation localization characteristics of rock‐like materials.

The Influence of Aggregate Microstructure on Tailings Behaviour

Conventional constitutive soil models applied in geotechnical engineering have been developed using the phenomenological approach from macroscopic observations and application of continuum mechanics. Despite the adopted simplification and homogenisation of complex interactions of soil particles, water and air, the phenomenological models and the underlying principles have been proven to satisfactorily describe the stress-strain conditions in most common soils. However, the application of the conventional soil behaviour models has been proven to be difficult in the mining industry and tailings storage facilities in particular, where the structural integrity of the storage facilities often depends on the performance of extensively altered materials (tailings) that are produced as a waste product from ore processing. The difficulties stem from the altered nature of the tailings and the inconsistencies in the tailings deposition, which may result in the formation of porous and brittle matrices of heterogeneous aggregates. Such matrices are susceptible to static and dynamic liquefaction whereby little changes in the stress-strain conditions can result in a sudden collapse of the soil structure. Sampling and preservation of intact delicate tailings is often unachievable, and the analyses of the laboratory tests are obscured by the simplifications, assumed homogenisation of the sample and the inherent influence of the testing apparatus on the measured properties. Therefore, the characterisation of the in situ conditions of the tailings and the prediction of the tailings performance for altering stress-strain conditions using conventional soil behaviour models is very difficult. Yet, understanding the delicate state of the brittle tailings is crucial for upstream and centrally raised tailings storage facilities. This is exemplified by the facility failures which featured devastating consequences in Brazil in 2015 and 2019. These failures were caused by liquefaction of tailings, which acted as foundations for the upstream raised embankments. This paper discusses the influence of the tailings micro-structure on the macroscopically observed behaviour. This paper also shows that, using modern optical and other testing methods, the micro-structure can be measured and then allowed for in the soil behaviour model with the aim to improve the reliability of tailings liquefaction assessment.

Method for absolute measurement of flat surface.

Interferometry is a relative measurement method for optical surface testing, and thus its testing accuracy depends on the accuracy of the reference surface. Absolute measurement is one of the most effective methods to improve the testing accuracy in interferometry. We present an efficient absolute measurement method based on Zernike polynomial fitting algorithms. With our proposed method, the profiles of both the test surface and the reference surface can be calculated simultaneously. We further carried out simulation analysis to scientifically evaluate the test accuracy of the proposed method. Finally, we conducted actual experiments to demonstrate the feasibility and practicability of our method.

Characterization of ceramics based on laser speckle photometry

Abstract. Advanced ceramic components are frequently used in industrial applications. As a brittle material, ceramic reacts very suddenly to excessively high stresses. Existing defects lead to rapid crack growth followed by spontaneous destruction. This leads to a functional failure of the entire component. It is therefore important to develop innovative techniques to ensure a good quality condition of ceramic products. Laser speckle photometry (LSP) is an optical nondestructive testing method. It is based on the dynamic analysis of time-resolved speckle patterns that are generated by an external excitation. In this paper, we will present two investigations on ceramic components using the LSP technique. One is the nondestructive stress characterization on ceramic surfaces, and the other is the defect detection on ceramics components. The aim is to improve the quality and safety control of ceramic production in the challenging industrial field. Preliminary results have shown the potential of the LSP sensor system for the nondestructive characterization of ceramics in terms of stress monitoring and surface defect detection.

Optical testing method analysis of carrier transport in GaAs PCSS

Measurement of the carrier transport in the GaAs photoconductive semiconductor switch (PCSS) is important for the study of the GaAs PCSS current filament and the design of improved GaAs PCSS devices. In this study, an optical testing method was proposed for the measurement of the time-dependent carrier density distribution in the GaAs PCSS. The measured electron density curves show that the carrier density distribution between the two electrodes is nonuniform for Δt = 0, and as Δt increase from 0.6 ns to 6 ns, a large number of carriers concentrate near the anode of the GaAs PCSS. These phenomena are analyzed in detail and the measured curves are found to be in good agreement with the simulation results.

Automatic fringe pattern enhancement using truly adaptive period-guided bidimensional empirical mode decomposition.

Fringe patterns encode the information about the result of a measurement performed via widely used optical full-field testing methods, e.g., interferometry, digital holographic microscopy, moiré techniques, structured illumination etc. Affected by the optical setup, changing environment and the sample itself fringe patterns are often corrupted with substantial noise, strong and uneven background illumination and exhibit low contrast. Fringe pattern enhancement, i.e., noise minimization and background term removal, at the pre-processing stage prior to the phase map calculation (for the measurement result decoding) is therefore essential to minimize the jeopardizing effect the mentioned error sources have on the optical measurement outcome. In this contribution we propose an automatic, robust and highly effective fringe pattern enhancement method based on the novel period-guided bidimensional empirical mode decomposition algorithm (PG-BEMD). The spatial distribution of the fringe period is estimated using the novel windowed approach and then serves as an indicator for the truly adaptive decomposition with the filter size locally adjusted to the fringe pattern density. In this way the fringe term is successfully extracted in a single (first) decomposition component alleviating the cumbersome mode mixing phenomenon and greatly simplifying the automatic signal reconstruction. Hence, the fringe term is dissected without the need for modes selection nor summation. The noise removal robustness is ensured employing the block matching 3D filtering of the fringe pattern prior to its decomposition. Performance validation against previously reported modified empirical mode decomposition techniques is provided using numerical simulations and experimental data verifying the versatility and effectiveness of the proposed approach.