High-speed Thermography Research Articles

How does heat generation affect the cut and chip wear of rubber?

Tire wear is a fracture process that has a decisive impact on tire life and on the environment. When a tire rolls, a heating process occurs due to friction caused by the viscoelastic rubber sliding over uneven road. This process occurs globally in the contact patch area and locally around the asperity tips, heating the tread and transferring heat to the surrounding material. On roads with a good quality pavement, the stress, and therefore the heat, is evenly distributed throughout the rubber material of the tire, which has a direct effect on fatigue wear. In contrast, unevenly distributed stress, and therefore heat, is generated in the tread when the tire rolls and slides over sharp asperities in rough terrain. This leads to very pronounced, unstable fracture processes that cause unevenly distributed wear, known as cut and chip (CC). The extent of heat generation or temperature evolution and its effect on CC wear have not yet been investigated and described in scientific publications. Therefore, this study firstly presents the detailed characterization of the influence of temperature development on the CC wear of a styrene–butadiene rubber, which commonly is used in treads of consumer tires. The investigations were carried out using the unique instrumented cut and chip technique in combination with a high-speed thermography.

Active thermography in PBF-LB/M with the synchronized path infrared thermography

This contribution presents a new technique for active thermography in laser powder bed fusion of metals (PBF-LB/M), utilizing the Synchronized Path Infrared Thermography (SPIT) setup. The approach uses the processing laser to thermally excite the surface of a stainless steel specimen allowing for in-situ non destructive testing. A secondary galvanometer scanner, optimized for MWIR radiation, in combination with a high-speed thermography system, is capable of conducting detailed subsurface defect analysis. The tests are carried out with artificially induced defects of varying sizes, the method uses temperature gradient analysis and higher order derivatives of the temperature profile along the laser path to identify undesirable thermal behavior. The findings highlight the potential of SPIT as a non-destructive and efficient tool for enhancing PBF-LB/M process monitoring, with implications for improved manufacturing quality and safety.

Investigating the Tooth Contact Based on a High-speed Thermography Monitoring Conducted Under High-reduction Hypoid Gears Meshing Condition

Investigating the Tooth Contact Based on a High-speed Thermography Monitoring Conducted Under High-reduction Hypoid Gears Meshing Condition

A novel apparatus dedicated to the estimation of the thermal diffusivity of metals at high temperature

In order to characterize thermophysical properties of high conductivity metallic materials, this work proposes a novel experimental apparatus supported by an analytical solution and a numerical simulation. The experimental set-up measures simultaneously the temperature evolutions on both the front and rear faces of a sample using a single detector following the high-speed thermography principle through a dedicated system of six mirrors. This innovative configuration allows to reach high temperatures in a controlled atmosphere without pollution by contact. A transient 2D-axisymmetric model is developed, considering heat transfer along the radius and thickness directions. In a first stage, the model is compared to a finite element model, then the estimation procedure is validated by a noised direct model. Afterwards, the experimental temperatures versus time are used to estimate the thermal diffusivity of pure iron and stainless steel 304 in the solid state at high temperature in a pollution-free environment. The estimated values for a temperature range between 1300 K and 1600 K are then compared with published data.

Pool boiling performance on the textured hemi-wicking surfaces fabricated by nanosecond laser ablation

Today the problem of the boiling improvement is directly related to the heating surface modification at the micro- and nanoscale. As was shown by different authors the hemi-wicking surfaces demonstrate extremely high enhancement of heat transfer (HTC) and critical heat flux density (CHF) during boiling. In this paper, the laser ablation technique was used to fabricate textured hemi-wicking silicon surfaces. This surface modification technique is one of the most promising and discussed techniques today due to its high accuracy, implementation ease and high stability of the fabricated surfaces. The effect of the laser type on the silicon surface properties and boiling improvement was studied in detail. The texturing was performed using lasers with different wavelength - infrared (1064 nm) and visible (532 nm), but with the same number of pulses per unit area and laser spot diameter. The experiments showed that the water pool boiling performance differs significantly depending on the type of laser treatment. In particular, while the usage of infrared laser results in the HTC enhancement up to 78% compared to the untreated surface, the visible laser-textured surface in contrast shows the deterioration of the heat transfer rate up to 40%. At the same time, the visible laser-textured surface demonstrates the maximum CHF value of 1806 kW/m2, which is more than 2 times higher than for the untreated surface. The comparison with the models showed, that such an enhancement is explained by the highest capillary wicking of this surface. Based on the analysis of departure diameters, nucleation frequencies and the conditions for the vapor bubbles formation the observed difference in the heat transfer rate during boiling was revealed. Also using the high-speed thermography the dynamics of reversible and irreversible dry spots was studied during boiling on laser-textured hemi-wicking surfaces for the first time.

Registration of Nonstationary Heat Flux Dynamics in Shock Tunnels Using High-Speed Thermography

Registration of Nonstationary Heat Flux Dynamics in Shock Tunnels Using High-Speed Thermography

Observation of Pattern Formation during Electromagnetic Levitation Using High-Speed Thermography

Electromagnetic levitation (EML) was employed for studying the velocity and morphology of the solidification front as a function of undercooling of metallic materials. The limitation of the EML technique with respect to low melting alloys that emit outside the visible light spectrum was overcome by employing state-of-the-art high-speed mid-wavelength infrared cameras (MWIR cameras) with a photon detector. Due to the additional thermography contrast provided by the emission contrast of the solid and liquid phases, conductor, and semi-conductor, the pattern formation of Al-based alloys was studied in detail, revealing information on the nucleation, phase selection during solidification, and the influence of convection.

Super-Resolution Thermal Imaging Using Uncooled Infrared Sensors for Non-Destructive Testing of Adhesively Bonded Joints

To compensate for the inability of inexpensive uncooled infrared (IR) sensors to perform high-speed thermography detection with low noise and high sensitivity in the field of non-destructive testing (NDT), a post-processing method for uncooled IR sensors based on compressive sensing is proposed in this paper to perform super-resolution NDT thermography. Super-resolution IR phase images can be generated by first using a sparse representation of the low-resolution (LR) IR images and a sparse dictionary generated from randomly sampled high-resolution (HR) raw training image patches to generate an HR IR image sequence, and, subsequently, implementing IR thermography NDT. To verify the reliability of the proposed method, super-resolution IR images were combined with pulsed phase thermography (PPT) to verify bonded joint structures in carbon fibre-reinforced polymer (CFRP). Compared to other methods, the proposed method reduces the mean square error (MSE) by 11.13% and yields a better visual effect on the PPT phase image reconstructed using three-fold super-resolution. The proposed method not only produces sharp defect edges, but also retains the original texture, which is expected to enable wider application of uncooled IR sensors in NDT applications in the future.

Infrared High-speed Thermography of Combustion Chamber Wall Impinged by Diesel Spray Flame

Infrared High-speed Thermography of Combustion Chamber Wall Impinged by Diesel Spray Flame

Evaluation of heat transfer within numerical models of resistance spot welding using high-speed thermography

The automotive industry is demanding more sophisticated resistance spot welding (RSW) models with an emphasis on integrated computational materials engineering (ICME) to better design welded structures. RSW process models are often validated using experimental weld nugget diameter measurements that verify the maximum temperature prediction but not the entire transient temperature response. The accuracy of temperature data on-cooling is essential to reduce error in integrated process-material models during the simulation of microstructural evolution. In this study, two existing 3D finite element (FE) models of RSW (general-purpose and RSW-dedicated) that were previously optimized for 1.5 mm thick Usibor®1500 steel are conventionally validated using experimental nugget diameter and electrode indentation measurements and then modified to represent half-section RSW. The half-section RSW simulation results are directly compared to experimental temperature data captured using high-speed thermography (HST). Analysis of HST showed that the thermal history and t8/5 predicted by RSW-dedicated model were more consistent with the HST data, but the general-purpose model more accurately predicted half-section RSW nugget diameter by 8 % and electrode indentation by 11 % as a function of welding current. The models’ material properties, specifically workpiece thermal conductivity and specific heat as a function of temperature, had a significant effect on the RSW model temperature fields on-cooling. Overall, HST of half-section RSW provided a quantitative comparison of experimental and simulated temperature results and was a viable technique to validate the thermal history outputted by RSW FE models.

Novel Calibration Strategy for Validation of Finite Element Thermal Analysis of Selective Laser Melting Process Using Bayesian Optimization.

Selective laser melting (SLM) produces a near-net-shaped product by scanning a concentrated high-power laser beam over a thin layer of metal powder to melt and solidify it. During the SLM process, the material temperature cyclically and sharply rises and falls. Thermal analyses using the finite element method help to understand such a complex thermal history to affect the microstructure, material properties, and performance. This paper proposes a novel calibration strategy for the heat source model to validate the thermal analysis. First, in-situ temperature measurement by high-speed thermography was conducted for the absorptivity calibration. Then, the accurate simulation error was defined by processing the cross-sectional bead shape images by the experimental observations and simulations. In order to minimize the error, the optimal shape parameters of the heat source model were efficiently found by using Bayesian optimization. Bayesian optimization allowed us to find the optimal parameters with an error of less than 4% within 50 iterations of the thermal simulations. It demonstrated that our novel calibration strategy with Bayesian optimization can be effective to improve the accuracy of predicting the temperature field during the SLM process and to save the computational costs for the heat source model optimization.

Laser texturing of silicon surface to enhance nucleate pool boiling heat transfer

• The laser texturing technique is used to modify the silicon-based heat exchange surface. • Modified surface is characterized by superhydrophilic properties and high stability. • The laser-textured surface demonstrates the heat transfer enhancement during water pool boiling. • The surface modification leads to the considerable change in the dynamics of vapor bubbles. The surface modification is one of the most promising and discussed methods to improve the boiling performance. To date there are a lot of techniques to modify a heating surface, but the search for the optimal, simple and reliable one is still an actual problem. Recently, the surface texturing using laser ablation was applied in a number of studies, which showed its great potential for heat transfer enhancement and critical heat fluxes increase during pool boiling on the metal surfaces. In this paper, we modified a silicon surface by laser texturing and analyzed its effect on the heat transfer and bubble dynamics during water pool boiling using high-speed thermography and video recording. The experiments showed that the usage of laser-textured surface results in the heat transfer enhancement up to 49.5% compared to the reference rough silicon sample and up to 234% compared to the polished sample. Moreover, the modified surface is characterized with lower onset of nucleate boiling and lower bubble nucleation temperature. Dataset on the major characteristics of bubbles dynamics during boiling on the untreated and laser-textured surfaces was obtained using the high-speed video recording. Its analysis showed that the laser treatment leads to the significant increase in the nucleation site density and nucleation frequency, while the bubble departure diameter value dramatically decreases compared to the reference surface. On the basis of experimental data the relationship between nucleation frequency and departure diameter was found and analyzed both for untreated surface and for laser-textured one.

Infrared high-speed thermography of combustion chamber wall impinged by diesel spray flame

As a demonstration of a new method to examine the extremely unsteady and spatially varying wall heat transfer phenomena on diesel engine combustion chamber wall, high-speed imaging of infrared thermal radiation from the wall surface impinged by a diesel spray flame was attempted using a high-speed infrared camera. A 35 mm-diameter chromium-coated quartz window surface was impinged by a diesel spray flame with an impinging distance of 27 mm from the nozzle orifice in a constant volume combustion chamber. The infrared thermal radiation from the back surface of the 0.6 µm thick chromium layer was successfully visualized at 10 kHz frame rate and 128 × 128 pixel resolution through the quartz window. The infrared radiation exhibited coherent and streaky structure with radial stripes extending and waving from the stagnation point. The width of the radial stripes, spatial amplitude and the period of the waving movement were comparable to the ones for turbulent heat transfer on the engine cylinder wall previously measured with a heat flux sensor, suggesting that they are resulting from the turbulent structure in the wall-impinging diesel flame. The radiation intensity was calibrated to temperature and converted to heat flux via 3-D numerical analysis of transient thermal conduction in the quartz window. The peak-to-peak variation amplitudes of temperature and heat flux among the radial stripes during the diesel spray flame impingement were about 20 K and 2.3 MW/m2, corresponding to 13% of 150 K maximum temperature swing amplitude and 18 MW/m2 maximum heat flux, respectively.

In Situ Thermography During Laser Powder Bed Fusion of a Nickel Superalloy 625 Artifact with Various Overhangs and Supports.

This document provides details on the experiment and associated measurement files available fordownload in the dataset “In Situ Thermography During Laser Powder Bed Fusion of a Nickel Superalloy 625 Artifact with Various Overhangs and Supports.” The measurements were acquired during the fabrication of a small nickel superalloy 625 (IN625) artifact using a commercial laser powder bed fusion (LPBF) system. The artifact consists of two half-arch features with increasing slopes for overhangs. These overhangs range from 5° from vertical to 85° from vertical in increments of 10°. The artifact geometry and process are controlled to ensure consistent processing along the overhang geometry. This control enables the effect of overhang geometry and support structures to be isolated from effects of inter-layer scan strategy variations. The measurements include high-speed thermography of each layer, from which radiance temperature, cooling rate, and melt pool length are calculated.

Effects of Shaft Offset on Vibration and Tooth Contact Area Based on High-Speed Thermography Monitoring under Hypoid Gear Meshing Conditions

Effects of Shaft Offset on Vibration and Tooth Contact Area Based on High-Speed Thermography Monitoring under Hypoid Gear Meshing Conditions

Heat transfer mechanisms in pool boiling of water investigated by high-speed thermography

Heat transfer mechanisms in pool boiling of water investigated by high-speed thermography

Velocity-Field Measurements in a Fluid Boundary Layer Based on High-Speed Thermography

A new method of visualization of the flow-velocity fields within a boundary layer of a nonisothermal fluid using seedless velocimetry is proposed. The method is based on the high-speed thermographic detection of the dynamics of temperature inhomogeneities acting as a passive flow tracer through an infrared-transparent wall. As a result of thermal image post-processing using a cross-correlation algorithm, the fields of velocity of near-wall flow formed in the region of interaction between the submerged impinging water jet and the impinged surface are investigated in the range from 0 to 1 m/s, and the location of the laminar–turbulent transition inside the boundary layer are determined.

Accurate determination of laser spot position during laser powder bed fusion process thermography

High-speed thermography is useful tool for researching the laser powder bed fusion process by providing thermal information in heat affected zone. However, it is not directly possible to ascertain the position of the laser spot with respect to the melt pool, which could provide key information regarding how laser energy is distributed and absorbed.In this paper, we demonstrate a procedure for registering the laser spot position with the melt pool using a bright illumination source co-axially aligned with the laser to project a sharp spot on the build plane. This spot is fixed to the laser position and used as a reference frame for registering the laser spot with the melt pool radiance temperature distribution. Measurement results demonstrate the effect of varying process parameters (laser power and scan speed) on the melt pool thermal field and respective position of the laser spot.

Determination of the Thermal Diffusivity of Materials by a Nondestructive Express Method with the Use of Step-By-Step Local Heating of the Surface and High-Speed Thermography

We propose an express method for measuring the thermal diffusivity of the materials of products that does not require cutting out of the samples of special shapes from the homogeneous mass of the product. The method is based on the local heating of the surface by step-function pulses, e.g., by a focused laser beam with simultaneous high-speed thermography performed with the help of a thermal imager. The subsequent processing of a radially symmetric picture of isotherms carried out by using an original software program makes it possible to find the thermal diffusivity of macrohomogeneous materials with an error lower than 10%. As an example, we present the results of measurements of the thermal diffusivity of the ZrO2:MgO ceramics, PhenoCure Powder composite based on phenol formaldehyde resin, and TPK-5PD polymeric-rubber material.

Surface Temperature Analysis of Transversal Magnetic Field Contacts Using a Thermography Camera

Some vacuum interrupters (VIs) are equipped with transversal magnetic field contacts. A transversal directed Lorentz force makes the arc move circularly. The local surface temperature of the arc root is usually above the melting point at high current. The temperature of the heated and molten contact surface of a VI can be measured using a high-speed thermography camera. We present a methodology for determining the surface temperature. For this purpose, the emissivity of the contact material must be known. For Cu, we determined the emissivity at $\varepsilon _{\mathrm {liq}} = 0.053$ (liquid) and $\varepsilon _{\mathrm {sol}} = 0.035$ (solid) for a spectral wavelength range of 1.5–1.7 $\mu \text{m}$ . Switching tests were performed using spiral contacts (CuCr 75/25) with a diameter of 68 mm and a 50-Hz half-wave sinusoidal current of 19 kA (rms). We examined the temperature of cooling anode spots of two different switching tests with various arc burning times and arc diameter. During the cooling phase of the anode spots, we observed a plateau in temperature at both measurements with different slope and duration. The plateaus started at the liquidus temperature of 1903 K of CuCr 75/25.