Step Heating Research Articles

Depth detection of spar cap defects in large-scale wind turbine blades based on a 3D heat conduction model using step heating infrared thermography

The defects dispersed in a spar cap often lead to the failure of large-scale wind turbine blades. To predict the residual service life of the blade and make the repair, it is necessary to detect the depth of spar cap defects. Step-heating thermography (SHT) is a common infrared technique in this domain. However, the existing methods of SHT on defect depth detection are generally based on 1D models, which are unable to accurately detect the depth of spar cap defects due to ignoring material anisotropy and in-plane heat flow. To improve the depth detection accuracy of spar cap defects, a 3D model based on the theory of heat transfer is established by using the equivalent source method (ESM), and a defect depth criterion is proposed based on the analytical solution of the heat conduction equation. The modeling process is as follows. The heat conduction model of SHT was established by ESM. Then, coordinate transformation, variables separation, and Laplace transformation were utilized to solve the 3D heat conduction equation. A defect depth criterion was proposed based on emerging contrast Cr. A glass fiber reinforced plastic composite plate containing 12 square flat-bottom holes with different sizes and depths was manufactured to represent a spar cap with large thermal resistance defects, such as delamination and cracks. The experimental results demonstrate the validity of the 3D model. Then, the model was applied to an on-site SHT test of a 1.5 MW wind turbine blade. The test results prove that the depth detection accuracy of spar cap defects can be significantly improved by using the 3D model. In addition, by using an improved principle component analysis (PCA) method containing a contrast enhancement factor, artifacts can be reduced and the recognition time of defects can be shortened. The 3D model provides a tool for detecting the depth of deep-lying defects in a thick composite structure, and the SHT technology is optimized by improved PCA.

An outline of Paleoproterozoic-Mesoproterozoic crustal evolution of the NW Amazon craton and implications for the Columbia Supercontinent

ABSTRACT The Rio Negro Province in the NW Amazon craton is composed of three domains (northeastern, central, and southwestern) in turn separated into several regional terrains, showing main NE-SW and WNW-ESE structures and being composed of high-grade polydeformed basement with 1840–1700 Ma protolith ages. The Northeastern Domain shows basements dominated by high-K calc-alkaline to shoshonitic metagranitoids, orthogneisses, migmatites, augen gneisses, and local A-type leucogneisses (1810–1760 Ma, Cauaburi Complex). In Venezuela, this basement is not widely known, but encompasses the oldest rocks of the province (1840–1820 Ma, San Carlos Metamorphic Terrane). The Southwestern Domain comprises medium- to high-K calc-alkaline orthogneisses (Querari Complex) with an extended compositional range (diorite to granite), NE-trending main foliation, and 1740–1700 Ma protolith ages. The Central Domain comprises peraluminous crustal-derived granites (1520–1480 Ma), supracrustal rocks, paragneisses, and some Cauaburi Complex inliers. The Nd isotope data for the basement rocks indicates mantle sources with decreasing crustal contributions and younger TDM ages from east (2.54–1.96 Ga) to west (1.97–1.82 Ga). The Rio Negro Province is interpreted as an accretionary orogen formed by a long-lived magmatic arc system active during three phases: 1.84–1.82 Ga, 1.81–1.76 Ga (main flare up) and 1.75–1.70 Ga. Later, this arc system was affected by collisional orogenies at ~1500 Ma (Içana Orogeny) and ~1300 Ma (Putumayo Orogeny), as showed by the Ar–Ar step heating plateau ages (biotite, hornblende) and U-Pb SHRIMP ages (zircon, titanite) recording two main metamorphic events at 1520–1480 Ma (medium–high T) and 1400–1310 Ma (low–medium T), with important tectonothermal effects also further east in the Tapajós-Parima Province. Based on similar accretionary histories, the Rio Negro Province has also apparent long-lived connections with Laurentia and Baltica (Transscandinavian Belt), forming the core of the Columbia Supercontinent.

Non-destructive testing of delamination defects in GFRP patches using step heating thermography

Composite materials are extensively used for repairs in the different industries, where their quality is monitored by nondestructive testing. Through this work, the functional role of step-heating thermography on the detection of delamination defects in multi-layer GFRP composite patches are investigated. Specimens prepared for testing were GFRP patches of different thicknesses (4 and 8 layer laminates) which were mounted on to the aluminum plates. In order to create interlaminar separation, kepton sheets of miscellaneous sizes were incorporated between the laminas, during the patch manufacturing. The defects were arranged at the edge and center of different layers, simultaneously. After applying of step heating by using of flash lamps to the manufactured samples, the factors affecting the defect identification (thermal intensity and size difference percentage) were investigated. The results showed that all defects in both 4 and 8 layer laminates were identified in the thermal images were the dimensional accuracy of the defect size was 30% higher in 8 layer patch due to the lesser reflection of heat to the IR camera.

Formation behavior of oxygen precipitates in silicon wafers subjected to ultra-high-temperature rapid thermal process

In this study, we investigated the formation behavior of oxygen precipitates in Si wafers after a rapid thermal process (RTP) at 1350 °C in an oxygen atmosphere through experiments and simulations. The oxygen precipitate density varied based on the temperature (750–950 °C) and duration (0.5–16 h) of the first step of the two-step heat treatment after RTP. The highest oxygen precipitate density was achieved when the first-step temperature was set to 850 °C, and the second-step temperature was fixed at 1000 °C. The simulation consisted of the calculation of the depth profiles of the residual vacancy concentrations after RTP and oxygen precipitation during the two-step heat treatment after RTP. An empirical formula, in which the nucleation rate of the oxygen precipitates was assumed to be proportional to the fourth power of the residual vacancy concentration, was used in the temperature range of 600–1000 °C. In addition, we assumed that interstitial Si atoms, which were generated by the growth of the oxygen precipitates, consumed the residual vacancies through pair annihilation, thus stopping oxygen precipitation owing to the depletion of the residual vacancies. The simulation effectively reproduced the variations in the oxygen precipitate densities under different conditions in the first step of the heat treatment. Considering the results of the simulation, we concluded that the resulting oxygen precipitate density was determined by the nucleation rate, growth size, and timing of the terminal point of the nucleation.

Single step synthesis and heat effect on structure of new type nanostructured zirconia based solid electrolyte

Single step synthesis and heat effect on structure of new type nanostructured zirconia based solid electrolyte

Анализ методик измерения равновесных условий образования газовых гидратов

In this work, we analyze the factors that affect the experimental determination of the gas hydrate equilibrium conditions in various systems using step heating and ramp heating by GHA350 stirred autoclave or RCS6 rocking cells. It has been found that more reliable results are obtained using the GHA350 autoclave, which provides a more intensive mixing of the fluids. Step heatingis a priori a more reliable way to determine the equilibrium conditions of hydrate formation, suitable for any system. However, its application is time-consuming. An alternative heating method at a constant rate of 0.1-1 deg./h can significantly reducethe time of one measurement. However, when using it, to obtain reliable experimental data, it is necessary to select the heating rate considering the mixing efficiency of the setup used, the type of system under study, and other factors. For most systems, the results of measuring the hydrate equilibrium temperatures by step and continuous heating at 0.1 deg./h using GHA350 autoclaveare consistent within the measurement error. A greater discrepancy between the methods is observed for gas hydrates in concentrated salt solutions, which have a high viscosity at low temperatures.

Sustainable Heat-setting Process in Stenter for Textile Industry

Knitting, dyeing and finishing are the main steps in knit fabric processing. In finishing, Stenter machine is used to dry and heat-setting of fabrics. Generally one step heating process is running in most of the knit industries where knit fabrics in wet condition pass through very hot chambers (80–200 °C) in stenter which needs to slow the machine speed to evaporate water completely and deliver low production ultimately. Instead of one step heating, in this research two steps drying process like simple steam heated roller drying before chambers at low temperature (50–80 °C) and then drying, heat setting at higher temperature (80–200 °C) in chambers successfully increase the speed of stenter as well as production. Fabrics characterization shows that the properties of predried fabrics remain unchanged.

Accuracy improvement of the transient heater foil technique for heat transfer tests: preliminary results

Experimental heat transfer measurements are used in a wide range of fields, for example to validate new cooling concepts in turbomachinery, to assess the performances of heat exchangers, and to provide data for numerical simulations. A particular challenge is posed by complex geometries, where the heat transfer coefficients cannot be determined with the usual transient heater mesh method. One way to address these complex systems is the transient heater foil method, which generates a constant heat flux in the metal foil, which is attached at the surface to be measured. However, the accuracy of the measurement remains an open issue compared to the heater mesh method. Here we show a modification of the heater foil method, which uses a linearly increasing heat flux in the foil to improve the measurement accuracy, especially in low heat transfer regions. The new method is presented using a single impingement cooling setup; results demonstrate good agreement with the baseline method (heater foil with step heating) and the literature, while the accuracy is improved.

An Investigation on the Activation Energy and Thermal Degradation of Biocomposites of Jute/Bagasse/Coir/Nano TiO2/Epoxy‐Reinforced Polyaramid Fibers

Polyaramid is a type of aromatic polyamide that is used to strengthen materials due to its great thermal stability. The effect of adding 2 wt% of nano titanium oxide and 5% polyaramid fibers to an epoxy matrix composite reinforced with three distinct natural fibers (jute, bagasse, and coir fibers) on the structure and characteristics of the composite was examined in this study. Hand lay‐up approach was used to manufacture 40 wt. percent each fiber, separately reinforced biocomposites with the addition of polyaramid, and TGA experiments were used to investigate the thermal stability of jute/bagasse/coir composites with polyaramid. The thermal degradation of the polymer took place in five steps, according to the Broido plots, with the second step being the slowest and rate determining. Because less energy is used to remove hemicellulose and loosely binding water contained in bagasse fiber, Broido plots revealed that the first step heat degradation had the lowest activation energy (Ea).

Distance Effect in Transient Thermography for Internal Defects Detection in Composites

Composite materials are commonly used in industrial systems for their superior physical and chemical properties. Due to the necessity for safety distance in industrial systems, non-destructive testing (NDT) for composites at long distances provides an important guarantee for prompt detection of internal equipment failures. The existing long-distance inspection methods are mostly passive NDT techniques. In this paper, a long-distance NDT method based on transient thermography is proposed. A theoretical model is established that integrates the transient thermography approach with the thermographic distance effect, providing the theoretical foundation for research based on distance detection effects. Different thermal wave features are extracted based on thermal physical parameters in the time and frequency domains, and the detection effect is compared based on different feature images. By conducting experiments on SIR–GFE bonded plate with artificially simulated internal defects, the effectiveness of both pulse thermography (PT) and step heating thermography (SHT) in long-distance inspection was compared, in which the SHT method was superior. The detection effect of feature images at different distances are compared using the SHT technique, the model’s validity is tested, and the law of the function of distance in transient thermal imaging detection is derived. This work introduces the influence of distance in transient thermography for the first time, and it is hoped that this research can effectively guide and improve real industrial inspection.

Experimental study of flow boiling heat transfer and pressure drop in stepped oblique-finned microchannel heat sink

Oblique-finned microchannels have been reported to enhance heat transfer performance and suppress the flow boiling instability, but they can also cause an increase in pressure drop. Since the stepped microchannels are beneficial to reduce the pressure drop with enhanced heat transfer, herein we designed stepped oblique-finned microchannels (SOFMC) that uptake the comprehensive merit of oblique fins and steps, and compared the heat transfer and fluid regime with rectangular microchannels (RMC). The visualization experiment was performed using deionized water as the coolant with the temperature of 25 °C at different mass fluxes (400 kg/m2s, 600 kg/m2s and 800 kg/m2s) for different heat fluxes varying from 13.6–418.8 W/cm2. The stratified slug flow and stratified annular flow were observed in SOFMC, which were essential to enhance the heat transfer. Compared to RMC, the SOFMC showed a better heat transfer performance and a smaller pressure drop at high heat flux. The increase of nucleation sites, intensive disturbance by oblique fins and additional flow area along the flow direction for bubbles provided by steps contributed to suppress the flow boiling instability and enhance the flow boiling heat transfer for SOFMC. The large pressure drop and severe flow boiling instabilities are the main problems for the further improvement of heat transfer performance; hence the integration of steps and oblique fins in the microchannels provides promising potential for high heat flux dissipation due to the enhancement of heat transfer, reduction of pressure drop and suppression of flow boiling instabilities.

The Influence of the Soaking Temperature Rotary Forging and Solution Heat Treatment on the Structural and Mechanical Behavior in Ni-Rich NiTi Alloy.

The structural and thermophysical characteristics of an Ni-rich NiTi alloy rod produced on a laboratory scale was studied. The soak temperature of the solution heat-treatment steps above 850 °C taking advantage of the precipitate dissolution to provide a matrix homogenization, but it takes many hours (24 to 48) when used without thermomechanical steps. Therefore, the suitable reheating to apply between the forging process steps is very important, because the product’s structural characteristics are dependent on the thermomechanical processing history, and the time required to expose the material to high temperatures during the processing is reduced. The structural characteristics were investigated after solution heat treatment at 900 °C and 950 °C for 120 min, and these heat treatments were compared with as-forged sample structural characteristics (one hot deformation step after 800 °C for a 30 min reheat stage). The phase-transformation temperatures were analyzed through differential scanning calorimetry (DSC), and the structural characterization was performed through synchrotron radiation-based X-ray diffraction (SR-XRD) at room temperature. It was observed that the solution heat treatment at 950 °C/120 min presents a lower martensitic reversion finish temperature (Af); the matrix was fully austenitic; and it had a hardness of about 226 HV. Thus, this condition is the most suitable for the reheating stages between the hot forging-process steps to be applied to this alloy to produce materials that can display a superelasticity effect, for applications such as crack sensors or orthodontic archwires.

Study of ALDH from Thermus thermophilus-Expression, Purification and Characterisation of the Non-Substrate Specific, Thermophilic Enzyme Displaying Both Dehydrogenase and Esterase Activity.

Aldehyde dehydrogenases (ALDH), found in all kingdoms of life, form a superfamily of enzymes that primarily catalyse the oxidation of aldehydes to form carboxylic acid products, while utilising the cofactor NAD(P)+. Some superfamily members can also act as esterases using p-nitrophenyl esters as substrates. The ALDHTt from Thermus thermophilus was recombinantly expressed in E. coli and purified to obtain high yields (approximately 15–20 mg/L) and purity utilising an efficient heat treatment step coupled with IMAC and gel filtration chromatography. The use of the heat treatment step proved critical, in its absence decreased yield of 40% was observed. Characterisation of the thermophilic ALDHTt led to optimum enzymatic working conditions of 50 °C, and a pH of 8. ALDHTt possesses dual enzymatic activity, with the ability to act as a dehydrogenase and an esterase. ALDHTt possesses broad substrate specificity, displaying activity for a range of aldehydes, most notably hexanal and the synthetic dialdehyde, terephthalaldehyde. Interestingly, para-substituted benzaldehydes could be processed efficiently, but ortho-substitution resulted in no catalytic activity. Similarly, ALDHTt displayed activity for two different esterase substrates, p-nitrophenyl acetate and p-nitrophenyl butyrate, but with activities of 22.9% and 8.9%, respectively, compared to the activity towards hexanal.

Cerium oxide containing canasite based glass-ceramics for dental applications: Crystallization behavior, mechanical and chemical properties

The present work aims to investigate the role of CeO2 (cerium oxide) on crystallization behavior, microstructural features as well as mechanical and chemical properties of canasite glass-ceramics for dental applications. The obtained results confirm that further addition of cerium oxide to the glass composition leads to a slight increase of crystallization temperatures and significant decrease of thermal expansion coefficients of the starting glasses. According to the Raman spectroscopy results, cerium ions increase the network connectivity of the parent glasses by increasing the number of bridging oxygens. During the two step heat treatment, the presence of cerium oxide favors crystallization of miserite (K(Ca,Ce)5Si8O22[(OH)F]2) besides calcium fluoride (CaF2) and canasite (Ca5Na4K2Si12O30F4) crystalline phases. Based on the microstructural observations, canasite crystals have the inter-locked blade-like morphology whereas crystals of miserite have the cubic like morphology. Among the studied glass-ceramics, Base-C2 showed the highest value of chemical durability as well as acceptable mechanical properties fulfilling the essential requirements as a restorative dental material.

Electrochemical- and mechanical stability of catalyst layers in anion exchange membrane water electrolysis

Anion exchange membrane (AEM) water electrolysis is considered a promising solution to future cost reduction of electrochemically produced hydrogen. We present an AEM water electrolyzer with CuCoOx as the anode catalyst and Aemion as membrane and electrode binder. Full cell experiments in pure water and 0.1 M KOH revealed that the optimum binder content depended on the type of electrolyte employed. Online dissolution measurements suggested that Aemion alone was not sufficient to establish an alkaline environment for thermodynamically stabilizing the synthesized CuCoOx in a neutral electrolyte feed. A feed of base is thus indispensable to ensure the thermodynamic stability of such non-noble catalyst materials. Particle loss and delamination of the catalyst layer during MEA operation could be reduced by employing a heat treatment step after electrode fabrication. This work summarizes possible degradation pathways for low-cost anodes in AEMWE, and mitigation strategies for enhanced system durability and performance.

Investigations of mechanical properties and deformation behaviors of the Cr modified Ti–Au shape memory alloys

In view of the population aging issues, the functional materials, Ti–Au–Cr shape memory alloys (SMAs), have been explored in this study for the crucial biomaterial applications. This ternary system was chosen for solving the hypersensitivity problem in the conventional SMAs containing Ni and also for its high X–ray contrast, which is an essential requirement in medical applications. Physical metallurgy methods were utilized for the specimen preparation and the fundamental properties and functional performances were also evaluated. Cold–workability was greatly improved with the Cr addition. The parent β–phase was stabilized by 4.5 at.% Cr alloying concentration, while the discrimination of the α′–martensite phase and the α′′–martensite phase at low Cr addition concentrations was clarified. Lattice parameters and the deformation strains were further calculated based on the results of the X–ray diffraction analysis. Most of the specimens possessed shape recovery upon heating, while the Ti–4.0Au–5.5Cr alloy showed an almost perfect shape recovery rate of 96.7%. Pseudoelastic behavior was observed in most of the alloys. The austenite transformation temperatures were determined by the step–by–step heating processes.

Pulse electrodeposited zinc sulfide as an eco-friendly buffer layer for the cadmium-free thin-film solar cells

Zinc sulfide (ZnS) is an emerging alternate n-type buffer layer for the cadmium-free thin-film solar cells. The present research adopts a unique mixture of glycerol and tartaric acid for the emergence of phase-pure ZnS during pulse electrodeposition . Besides, proper optimization of pulse parameters aid in producing crystalline ZnS films with no post-deposition heat treatment. The as-deposited films exhibit cubic ZnS as confirmed from X-Ray Diffraction (XRD) and micro-Raman analyses. The optical study reveals an average transmittance of 71% in the wavelength spread of 300–900 nm with a band gap of 3.8 eV. The n-type semiconducting behavior of ZnS is affirmed from the Mott-Schottky analysis and the flat band potential is inferred to be −1.0 V vs SCE . The crystalline ZnS films produced from the economic pulse electrodeposition method devoid of heat treatment step, with their demonstration as photoanode in photoelectrochemical cells are suitable for the relevant applications. • A room temperature electrodeposition process for ZnS with better control over the morphology and composition. • Phase-pure ZnS is obtained using pulse electrodeposition with no post heat-treatment. • A novel method using a blend of organic reagents, tartaric acid and glycerol in the electrolyte.

Well-Constrained Mineralization Ages by Integrated 40Ar/39Ar and U-Pb Dating Techniques for the Xitian W-Sn Polymetallic Deposit, South China

Abstract Mineralization ages of many mineral deposit types (such as orogenic Au, stratabound Cu, and Mississippi Valley-type Pb-Zn deposits) are still difficult to date by the traditional isotopic chronometry because of the lack of suitable minerals. We have made efforts to establish a widely suitable dating technique to determine ore formation ages using a high-precision 40Ar/39Ar method on ubiquitously present fluid inclusions in quartz, sphalerite, and other nonpotassium minerals from hydrothermal deposits. The Xitian W-Sn polymetallic deposit in central South China contains several minerals suitable for isotopic dating for interchronometer comparison. 40Ar/39Ar laser step heating of 16 micas from ore veins, greisen, and metallogenic granites yields flat age spectra and thus well-defined ore formation ages ranging from 152.4 ± 1.5 (2σ) to 148.1 ± 1.4 Ma with an average of 150.2 ± 0.6 Ma. 40Ar/39Ar progressive crushing of nine quartz samples produces well-defined isochron lines for their primary fluid inclusions corresponding to isochron ages of 153.7–149.9 Ma with an average of 151.6 ± 0.6 Ma. Cassiterites from three hand specimens have weighted mean 206Pb/238U ages of 151.5 ± 1.7 (2σ), 149.7 ± 2.1, and 151.7 ± 2.1 Ma. All these new geochronological dates and previous molybdenite Re-Os ages yield well-constrained mineralization ages of 153–148 Ma for the Xitian W-Sn polymetallic deposit, which also confirms conclusively that the quartz 40Ar/39Ar progressive crushing technique is a feasible, valid dating technique. Furthermore, significant age information on the secondary fluid inclusions is potentially obtained simultaneously by this technique. We expect that this novel dating technique will be widely applied to determine the geologic fluids trapped in minerals during hydrothermal mineralization, hydrocarbon accumulation, metamorphism, tectonic activities, and other geologic processes.

Estimation of delamination thickness in a multi-layered thermally thin structure by step heating thermography

The performance of a multi-layered structure is dependent upon its structural integrity. The main challenge posed to the structural integrity of such structures is the vulnerability of the interface to the formation of defects (like delamination, crack, void). Hence it becomes compelling to study such structures and propose methodologies that could detect and characterize the defects. This paper presents an approach to estimate the delamination thickness formed at the interface of a two-layered structure (a simple case of a multi-layered structure). An analytical expression of delamination thickness is derived using the electrical analogy approach. The saturation value of absolute thermal contrast, which is a characteristic feature of the thermal response of material or structure with defect under step heating has been used to derive the analytical expression of delamination thickness. The proposed approach is fast, simple, noncontact and devoid of extensive data handling. Simulations and experiments have been done to verify the approach. This approach can provide guidance during the design phase of multi-layered structures and aid in defining their failure threshold depending on the application. Additionally, it can also be implemented in manufacturing units during quality checks or can also be used for in situ defect characterization.

Grain growth behaviors during solution annealing based on the heterogeneous microstructure in hot rolled nuclear grade austenitic stainless steel

Series of solution annealing experiments and quasi in-situ observation were employed to investigate the grain growth behaviors based on the heterogeneous microstructure with deformation bands and dynamic recrystallization (DRX) grains in hot rolled 316H austenitic stainless steel (ASS). It was worked out that during early stage of direct heating at high temperature of above 1000℃, the initial static recrystallized grains with different sizes would nucleate rapidly on the deformation band and DRX grains. With the extension of holding time, they gradually grew up to develop into the grains with large size differences, during which the larger grains continued to swallow adjacent smaller grains even presenting abnormal annexation or growth. However, by adopting stepped heating from low to high temperature, the grains evenly grew and presented relatively uniform distribution, which provides new idea for regulating grain size in manufacturing heavy ASSs.