Non-contact Stress Research Articles

Dynamically Modulated GaN Whispering Gallery Lasing Mode for Strain Sensor

AbstractThe continuous development of strain sensors offers significant opportunities for improving human–machine interfaces and health monitoring. The dynamically modulated lasing mode is a novel approach to realize a flexible, noncontact, high color‐resolvability, high‐resolution, and ultrasensitive strain sensor. Here, a flexible strain sensor perceiving stress variations is reported via the dynamical regulation of a GaN whispering gallery lasing mode based on the piezoelectric effect. The refraction index of GaN shows a linear relationship with the applied external tensile strain, resulting in a redshift phenomenon of the lasing mode peak at room temperature due to the predominant function of the piezoelectric polarization in the GaN microwire. Compared with a strain sensor relying on the wavelength shift of a photoluminescence (PL) emission peak, the differences and advantages of a sensor based on the strain‐induced lasing mode variation are also investigated and analyzed systematically. This strain sensor may serve as an essential step toward the color mapping of mechanical signals by optical methods, with potential applications in color‐perceived touching sensing, noncontact stress measurement, laser modulation, and optical communication technologies.

Online and real-time accurate prediction of tempered glass surface stress during quenching process

In order to obtain tempered glass stress quickly and accurately, a new method is proposed for the prediction of glass stress during quenching process with non-contact, online, and real-time analysis technique. Based on the infrared scanning of real-time surface temperature during the glass quenching process, the nonlinear viscoelastic model of glass tempered was established to calculate programmatically the variation laws of glass surface stress during the quenching process. The results show that under different technical parameters, the surface temperature of glass decreases exponentially with time. The surface stress shows the tensile stress at the initial stage and transforms to compressive stress when the glass temperature is below conversion temperature. The compressive stress increases quickly and tends to be stable at about 15 s during quenching. Air pressure, air-grid height, and heating temperature significantly affect the stress of tempered glass, and the tapping speed does not affect the stress of tempered glass. Compared with the measured values by Grazing Angle Surface Polarimeter (GASP) stress meter, the absolute errors of online prediction results do not exceed 5 MPa, and the relative errors are no more than 5%. This research indicates that non-contact, online, and real-time stress prediction technology can be achieved during tempered glass process, which also provide a theoretical basis for the automatic control of the glass tempered parameters.

Non-contact stress measurement in PET preforms

ABSTRACTResidual stresses in PET preforms is thought to be an important cause in the stress cracking of blown bottles but there is no data yet that can be linked to stress and cracking. An important step in this link is the measurement of stresses in the preform base and neck region of the preforms. This paper reports on the usage of photoelastic methods to measure residual stresses in preforms. It is found that the residual stresses vary from preform to preform and how cracks develop is due to the qualitative and quantitative presence of residual stresses and its orientation.

Rail neutral temperature monitoring using non-contact photoluminescence Piezospectroscopy: A field study at high-speed rail track

A novel non-contact stress sensing method using the photoluminescence piezospectroscopy (PLPS) method was applied in full-scale field test at high-speed rail tracks. The fluorescence spectra of the aluminum oxide (α-Al2O3) were collected from different locations on bare thermite weld surface for about 1.5 days. Prominent α-Al2O3 signals (i.e., R1/R2 peaks) were observed with the very short measurement time of 0.01 s, which is preferable in mobile sensing applications. The kernel spectrum estimation (KSE) method was developed as a postprocessing technique to determine R1/R2 peak locations accurately. The R1/R2 time histories showed strong correlation with those of strain gauges mounted on the rail near the thermite welds. The piezospectroscopy coefficients were determined at −30.01 cm−1/GPa for R1 and –32.11 cm−1/GPa for R2, calibrated with the strain gauge measurements. Prior to the field test, a laboratory test was conducted to determine the R1/R2 zero-stress states using a pulverized thermite weld sample. The zero-stress state was determined at 14,404.99 cm−1 for R1 and 14,434.09 cm−1 for R2. Using these parameters, rail neutral temperature was determined at full-scale high-speed tracks based on the absolute rail stress measured with PLPS without additional field calibrations.

Non-contact residual stress analysis method with displacement measurements in the nanometric range by laser made material removal and SLM based beam conditioning on ceramic coatings

Residual stress levels induced during the process are one of the more relevant characteristics of thermal spray coatings. Therefore, there are different techniques, such as the x-ray diffractometry or the classical micro hole drilling and milling method, to analyse and optimize the thermal spray coating process in order to obtain a desired level of residual stresses on coatings. The state of the art of the new developed non-contact, quasi non-destructive residual stress analysis method is presented. The material removal is based on laser ablation and complex ablation geometries are possible by using a spatial light modulator (SLM) for beam conditioning. 3D deformations on the specimen surface are measured in the nanoscale range by high-resolution digital holographic interferometry. Numerical procedures using the finite differences method are performed in order to calculate the shape geometry and the calibration curves required for the residual stress calculation from the measured 3D displacements, coating-substrate material combination and the ablation geometry. Experimental results on thermal spray coatings are presented and discussed with comparative measurements by the hole-drilling method. The potentials and difficulties of the method are discussed.

Piezoelectric Effect Tuning on ZnO Microwire Whispering-Gallery Mode Lasing.

We report a dynamic tuning on coherent light emission wavelengths of single ZnO microwire by using the piezoelectric effect. Owing to the dominant role occupied by the piezoelectric polarization effect in the wurtzite-structure ZnO microwire, the effective dielectric constant (or refraction index) of the gain media was modulated toward an increasing trend by applying a tensile strain, resulting in a shift of the strain-mediated whispering-gallery mode (WGM) lasing at room temperature. Also, the strain required to resolve the spectra in the two operating types of PL and lasing were systematically analyzed and compared. Because of the narrow line width in the lasing mode, the strain-dependent spectral resolution was improved by an order of magnitude, making it feasible for achieving high-precision, ultrasensitive, and noncontact stress sensing. Our results have an important impact on laser modulation, optical communication, and optical sensing technology.

Detection of physical stress using multispectral imaging

This study explored the potential of multispectral imaging for detecting physical stress on humans. Multispectral images were obtained from recruited participants, and a max completion-based differential tissue oxygen saturation (StO2) algorithm model was proposed and established without background information. Further correlation analysis showed that multi-subject facial StO2 fluctuations have similar intra-class affective patterns under physical stress. The algorithm model was verified with respect to physical stress ground truth to classify the baseline and physical stress status. The algorithm implements non-contact, non-intervention, and background-free physical stress detection. The algorithm achieved promising results in the experiment with an accurate rate of higher than 90%, which will provide an excellent foundation for future industrialization. Experimental results demonstrated that multispectral imaging, as a non-invasive method, has the potential to identify physical stress on humans.

Noncontact stress measurement from bare UHPC surface using Raman piezospectroscopy

AbstractRaman piezospectroscopy was applied for noncontact stress measurement from bare ultrahigh‐performance concrete (UHPC). Microstructure and chemical characterization were conducted for 3 phases of UHPC samples, including unmixed concrete ingredients (Sample 1), cured concrete (Sample 2), and pulverized concrete (Sample 3). Rich contents of polycrystalline silica (quartz) were observed from all samples. The global and local piezospectroscopy coefficients were measured from compressive loading frame tests at 3.77 cm−1/GPa and 1.62–9.10 cm−1/GPa, respectively. The quartz fingerprint peak was observed at 460.50 cm−1 from stress‐free UHPC powder, which can be used as the zero‐stress state to determine absolute stress in existing concrete structures. The global absolute stress equation is presented using the global piezospectroscopy coefficient and the zero‐stress state.

Noncontact mobile sensing for absolute stress in rail using photoluminescence piezospectroscopy

A novel noncontact, mobile sensing technique to measure absolute stress in rail using photoluminescence piezospectroscopy is presented. Photoluminescence piezospectroscopy is a vibrational spectroscopy technique for chemical identification and stress measurement by focusing low-power laser on a substance surface. Thermite welding is a major welding method for continuous welded rail, which produces iron (Fe) and aluminum oxides (Al2O3) after aluminothermic reaction. Photoluminescence piezospectroscopy was used as a noncontact stress sensing method since photoluminescence piezospectroscopy has an excellent detectability for alpha-phase aluminum oxide (α-Al2O3). Using a portable photoluminescence piezospectroscopy system, a prominent α-Al2O3 signal was collected from the bare surface of thermite weld samples. A loading frame test was conducted to determine the piezospectroscopic coefficient of α-Al2O3 in thermite weld. A pulverization method is introduced to determine absolute stress from an existing rail sample. The experimental results show many advantages of this method over traditional methods to measure stress in rail as a mobile sensing method.

Magnetoelastic Effect-Based Transmissive Stress Detection for Steel Strips: Theory and Experiment

For the deficiencies of traditional stress detection methods for steel strips in industrial production, this paper proposes a non-contact stress detection scheme based on the magnetoelastic effect. The theoretical model of the transmission-type stress detection is established, in which the output voltage and the tested stress obey a linear relation. Then, a stress detection device is built for the experiment, and Q235 steel under uniaxial tension is tested as an example. The result shows that the output voltage rises linearly with the increase of the tensile stress, consistent with the theoretical prediction. To ensure the accuracy of the stress detection method in actual application, the temperature compensation, magnetic shielding and some other key technologies are investigated to reduce the interference of the external factors, such as environment temperature and surrounding magnetic field. The present research develops the theoretical and experimental foundations for the magnetic stress detection system, which can be used for online non-contact monitoring of strip flatness-related stress (tension distribution or longitudinal residual stress) in the steel strip rolling process, the quality evaluation of strip flatness after rolling, the life and safety assessment of metal construction and other industrial production links.

Non-destructive and non-contacting stress–strain characterization of aerospace metallic alloys using photo-thermo-mechanical radiometry

A photo-thermo-mechanical non-destructive inspection methodology was developed theoretically and experimentally for non-contact, non-destructive evaluation of mechanical stress–strain relations in metallic materials. A one-dimensional thermal-wave model modified to include mechanical stress explicitly was used to fit experimental data from both frequency scan and stress scan tests and determine the thermal effusivity and diffusivity of an aerospace-industry-relevant aluminum 6061 alloy. Within the elastic regime the thermal conductivity values measured from both photothermal radiometry (PTR) amplitude and phase showed very good agreement, thereby establishing the self-consistency of the new photo-thermo-mechanical radiometry (PTMR) method. Furthermore, a linear conductivity–stress dependence was found, thus establishing the dominant role this property plays in the ability of PTMR to monitor mechanical changes in the aluminum alloy. It was demonstrated that PTMR can be used as a non-contact “strain gauge” within and far beyond the operational strain range of commercial strain gauges, up to the fracture point.

Recurrent Knee Pain in a Teenage Dancer

HISTORY: A 13 y/o female was pivoting while playing with her friends and felt her right kneecap shift after a noncontact valgus stress. She had pain and swelling shortly after the injury, but was able to ambulate at that time with a limp. Anterior knee pain was minimal but persistent for several days. Use of a knee sleeve lessened the pain. At her initial clinic visit 5 days post-injury, she had a large joint effusion. She demonstrated full extension but flexion was limited to 95°. Tenderness was present at the medial patellar facet and over the retinaculum. Ligamentous and meniscal testing was negative. Radiographs obtained in the ED and clinic demonstrated a chronic appearing well corticated loose body suggestive of synovial osteochondromatosis. She was given a presumptive diagnosis of patellar subluxation, told to continue with brace use, and referred to physical therapy. PT gave her an HEP after one visit as her stability, strength, and range of motion were within normal limits. The athlete was lost to follow up for four months, but presented again to clinic after an instability event left her with a painful, swollen, right knee, with limited ROM and an inability to ambulate without crutches. Further history revealed that she had been experiencing “shifting” in her knee once or twice monthly while playing sports with minimal pain. PHYSICAL EXAMINATION: Examination of knee revealed a 2+ effusion. No focal tenderness to palpation. ROM was painful ranging from -10° extension to 110° flexion. Negative valgus/varus stress tests, McMurray’s, apprehension and grind tests were noted. Lachman’s testing was asymmetric with 1-2+ on the injured side but significant guarding and discomfort was noted by the patient who was somewhat uncooperative. DIFFERENTIAL DIAGNOSIS: 1) Recurrent Patellar Subluxation 2) Loose Body 3) ACL Injury TESTS AND RESULTS: MRI demonstrated: 1) Ossified loose body in the anterior compartment 2) Complete rupture of ACL 3) Diminutive medial meniscus, possible chronic tearing FINAL DIAGNOSIS: 1) ACL rupture with avulsion fx/loose body adherent to the ACL stump 2) Large bucket handle medial meniscus tear TREATMENT AND OUTCOMES: 1)ACL reconstruction with hamstring autograft with allograft augmentation 2)Repair of medial meniscus 3)Removal of loose body with ACL debridement

Portable Piezospectroscopy system: non-contact in-situ stress sensing through high resolution photo-luminescent mapping

Through the piezospectroscopic effect, certain photo-luminescent materials, once excited with a laser, produce spectral emissions which are sensitive to the stress or strain that the material experiences. A system that utilizes the piezospectroscopic effect for non-contact stress detection over a material's surface can capture important information on the evolution of mechanical response under various conditions. Therefore, the components necessary for piezospectroscopic mapping and analysis have now been integrated into a versatile and transportable system that can be used with photo-luminescent materials in any load frame or on a variety of structures. This system combines compact hardware components such as a portable laser source, fiber optics, spectrograph, charge-coupled device (CCD), and an X-Y-Z stage (with focusing capabilities) with a series of data analysis algorithms capable of analyzing and outputting high resolution photo-luminescent (PL) maps on-site. Through a proof of concept experiment using a compressed polycrystalline alumina sample with sharp machined corners, this system successfully captured high resolution PL maps with a step size of 28.86μm/pixel and located high stress concentrations in critical areas, which correlated closely with the results of a finite element model. This work represents an important step in advancing the portability of piezospectroscopy for in-situ and non-contact stress detection. The instrumentation developed here has strong implications for the future of non-destructive evaluation and non-invasive structural health monitoring.

Ultra-Thin SiO2/Si Interface Quality In-Line Monitoring Using Multiwavelength Room Temperature Photoluminescence and Raman Spectroscopy

Multiwavelength room temperature photoluminescence (RTPL) and Raman spectroscopy were proposed as in-line monitoring techniques for characterizing the dielectric/Si interface. As an application example, ∼7.0 nm thick ultra-thin SiO2 films on 300 mm Si wafers, prepared by various oxidation techniques and conditions, were characterized using multiwavelength RTPL and Raman spectroscopy. Specifically, overall quality of the ultra-thin SiO2/Si interface (including passivation characteristics) and Si lattice stress beneath SiO2 films are investigated. The overall SiO2/Si interface quality was seen to be very dependent on oxidation technique and process conditions. Within wafer and wafer-to-wafer variations of SiO2/Si interface quality were successfully characterized by RTPL and Raman spectra measurements. For electrical analysis of SiO2/Si-based structures, non-contact corona charge-based, in-line (capacitance-voltage (C-V) and stress induced leakage current (SILC)) measurements were performed and compared with RTPL and Raman characterization results. Surprisingly, significant variations in RTPL intensity at and near the corona charge-based measurement sites, indicated that the corona-based electrical measurement technique, though non-contact, was indeed invasive. The effect of corona-charge based electrical measurements on SiO2/Si interface was permanent and even clearly visible from the back side of the wafer. RTPL intensity variations at and near the measurement sites remained, even after a forming gas anneal.

A focused electric spark source for non-contact stress wave excitation in solids.

A focused electric spark is used as a non-contact acoustic source to excite stress waves in solids. The source consists of an electric spark source located at the near focus of an ellipsoidal reflector that focuses the acoustic disturbance generated by the spark source to the far focal point. Experimental studies using both contact and non-contact sensors indicate that the source has the capability to excite the Rayleigh surface wave and impact-echo mode (S1-zero-group-velocity Lamb mode) in a 250 mm thick concrete slab and to enable fully air-coupled testing of concrete specimens.

Thermoelastic Stress Analysis - Emerging Opportunities in Structural Health Monitoring

The emergence recently of a thermoelastic stress analysis (TSA) capability exploiting low-cost, compact and rugged microbolometer detector technology provides a significant opportunity topromote a broader use of this powerful non-contact full-field stress analysis technique. An area whereit has considerable and hitherto unexplored potential is in in-situ structural health monitoring (SHM).The present paper outlines the case for a nexus between SHMand TSA in this new form. It is proposedthat the approach should yield diagnostic and prognostic capabilities surpassing those of some existingSHM modalities. An F/A-18 centre-fuselage full-scale structural fatigue test is employed as a casestudy to illustrate the practical feasibility of the approach and to underscore some of its potential.Although the case study focuses on an aircraft structure, the concept has potential application to awide variety of different engineering assets across the aerospace, civil and maritime sectors.

Non-contact stress measurement in granular materials via neutron and X-ray diffraction: theoretical foundations

Model validation remains a serious problem within the field of computational granular materials research. In all cases the rigor of the validation process is entirely dependent on the quality and depth of the experimental data that forms the point of comparison. Neutron and X-ray diffraction methods offer the only quantitative non-contact method for determining the spatially resolved triaxial stress field within granular materials under load. Measurements such as this can provide an unprecedented level of detail that will be invaluable in validating many models. In this paper the theoretical foundation underpinning diffraction-based strain measurements, their conversion to local stress in the particles and ultimately into the bulk stress field is developed. Effects such as elastic anisotropy within the particles of the granular material, particle plasticity and locally inhomogeneous stress distribution are shown to not offer any obstacles to the method and a detailed treatment of the calculation of the bulk stresses from the particle stresses is given.

Stress-induced magnetic hysteresis in amorphous microwires probed by microwave giant magnetoimpedance measurements

We report the results of a detailed study of the effects of tensile and torsional stresses on the giant magnetoimpedance (GMI) characteristics of vanishing-magnetostrictive Co-rich microwires at microwave frequency. A complex stress-induced hysteresis behaviour is identified in the GMI response in the presence of tensile and torsional stresses. It is also revealed that there exists a competition between these two kinds of stresses on the critical field via the interactions with the intrinsic anisotropy. An “enhanced core-shell” model is proposed here to resolve the physical origin of the low-field hysteresis and the dependence of induced anisotropy field on the applied tensile and/or torsional stress. Our results are of both technical importance to the design of non-contact stress sensors exploiting the GMI of microwires and fundamental significance to the understanding of the microwave GMI characteristics of soft magnetic microwires in the presence of external stresses.

A novel stress monitoring method through stress-induced respiratory alterations: non-contact measurement of respiratory V(T)/T(I) alterations induced by stressful sound using a 10 GHz microwave radar

We have developed a non-contact stress monitoring system which measures respiratory V(T)/T(I) (tidal volume/inspiration time) alterations using a 10 GHz microwave radar. The measurable distance of the system is 50 cm, which is 10 times longer than our previously developed stress monitoring system which measures heart rate variability using a 24-GHz microwave-radar. The study was conducted with eight subjects (23 ± 1years old) to evaluate the efficacy of the system. An audio stimulus at 95 dB sound pressure level was presented to the subjects following a silent period of 120 seconds. During the silent period, V(T)/T(I) averaged 826 ± 384 ml s−1, while it increased significantly (p < 0.05) with an average of 1227 ± 704 ml s−1 during audio stimulus low frequency component (LF)/high frequency component (HF), which reflects sympatho-vagal valance, showed a peak during audio stimuli. This paper aims to study the efficacy of the non-contact stress monitoring system for its future applications in many fields including health and safety.

OS0206 蛍光現象を利用した非接触応力測定法に関する研究(放射光およびEBSD法による材料評価,OS-2 回折法による材料評価)

OS0206 蛍光現象を利用した非接触応力測定法に関する研究(放射光およびEBSD法による材料評価,OS-2 回折法による材料評価)