Search

In this study, the monocrystalline silicon (c-Si) solar cell irradiated by 100 KeV proton beams at various fluences is investigated. A one-dimensional two-layer carrier density wave model has been developed to estimate the minority carrier lifetime of n-region and p-region of the non-irradiated c-Si solar cell by best fitting with the experimental photocarrier radiometry (PCR) signal (the amplitude and the phase). Furthermore, the lifetime is used to determine the initial defect density of the quasi-neutral region (QNR) of the solar cell to predict its I–V characteristics. The theoretically predicted short-circuit current density (Jsc), and open-circuit voltage (Voc) of the non-irradiated samples are in good agreement with experiment. Then a three-region defect distribution model for the c-Si solar cell irradiated by proton beams is carried out to describe the defect density distribution according to Monte Carlo simulation results and the initial defect density of the non-irradiated sample. Finally, we find that the electrical measurements of Jsc and Voc of the solar cells irradiated at different fluences using 100 KeV proton beams are consistent with the PCR predicting results.

An inverse analysis methodology is developed to simultaneously identify the thermal diffusivities and subsurface defect of carbon fiber reinforced polymer (CFRP) laminate through lock-in thermographic phase (LITP) profile reconstruction. A hybrid algorithm that combines simulation annealing algorithm (SA) and Nelder–Mead simplex search method (NM) is proposed to minimize the objective function constructed by LITP profile for determination of the thermal diffusivities ( α x and α z ) and subsurface defect characteristics (size D and depth H D ). For the hybrid method, SA is used to find a better feasible initial-guessed solution for NM. Numerical examples show that LITP has the merit of identifying the thermal diffusivities of CFRP laminate by inverse analysis. In comparison with SA and NM, respectively, the hybrid method can be converged to yield good estimates faster and more efficiently. Experimental and simulation LITP of defective regions are used to determine the thermal diffusivities and the size and depth of subsurface defect. The results show that the estimated thermal diffusivities and the size and depth of defect are in good agreement with the reference values, and the relative deviations are less than 5%. Nevertheless, this approach can only be applied for the determination of thermal diffusivities of CFRP laminate with subsurface defect.

In this work, an extension laser beam was used as heating source to evaluate the composite material by active thermographic method. In particular, a series of carbon-fiber-reinforced polymer (CFRP) specimens with various depth and sizes of flat-bottom holes (FBH) were inspected using lock-in thermography (LIT). The quantitative LIT phase was employed to identification the subsurface defect using the phase decision threshold (PDT, a phase deference between defective area and the sound one), and then the detectable and undetectable defects were expressed as 1 and 0 (hit/miss data), respectively. The POD curves of continuous phase response data and the hit/miss data processing were used for estimation the detection capability and reliability of LIT phase image for NDI&E of CFRP composites, and the effects of PDT value and modulation frequency on POD curves were compared.

An inverse heat transfer approach is developed to characterize the size and depth of subsurface defects in CFRP composite materials through the reconstruction phase profile of lock-in thermography (LIT) obtained by finite element simulation. This work mainly focuses on the application of hybrid method that integrates simulation annealing algorithm (SA) and Nelder–Mead simplex search method (NM) for determination of the sizes and depths of subsurface defects within the CFRP laminate materials. For this purpose, an 808 nm laser is used for imposing a modulated heat excitation on the CFRP laminate specimen, and the thermal images are collected using an infrared camera. The hybrid method is employed to find the optimal solutions of the objective or cost function constructed by phase profile of LIT between an experimental configuration and numerical solution for a CFRP specimen. The experimental results show that the size and depth of subsurface defects are effectively obtained through inverse solving the constructed objective or cost function by the hybrid method. The estimated maximum errors for the size and depth are less than 5% and 4% for given subsurface defects by the proposed method, respectively.

The pulsed thermographic technique was used to detect flat-bottomed hole defects in CFRP sheet. Pulsed phase thermography (PPT) was used to extract the characteristic information of the thermal wave signal generated by thermal pulse. The difference of the phases between the sound and defective areas were analyzed. The defects’ edges were extracted by Fuzzy C-Means clustering algorithm.

An investigation on SiC coated carbon–carbon (C/C) composite plates has been undertaken by pulsed thermography. The heat transfer model has been built and the finite element method (FEM) is applied to solve the thermal model. The simulation results show that defects with DA/DP smaller than one can hardly be detected by an infrared camera with the sensitivity of 0.02 °C. Certificated experiments were performed on the built pulsed thermography system. The thermal wave signals have been processed by subtracting background image method (SBIM), pulsed phase thermography (PPT), and temperature–time logarithm fitting method (TtLFM). The limit DA/DP of defects in SiC coated C/C composite plates with the thickness of 6 mm that can be detected by pulsed thermography with the presented signal analysis algorithms has been obtained.

Active infrared thermographic technique was used as a non-destructive inspection (NDI) tool for carbon–carbon (C/C) composite with subsurface defects. A serial of representative carbon–carbon composite test samples, consisting of cutouts and cracks as defects were investigated experimentally and analyzed using finite element method (FEM). Both transient pulsed thermography and lock-in thermography technique were investigated. The capability of two techniques to detect subsurface defects of C/C composite and to provide information about the location of defect was analyzed. Results indicate that active thermographic technique is available for the subsurface defect detection of carbon–carbon composite.

An investigation into the effect of size on the quantitative estimation of defect depth in a SiC coated carbon–carbon (C/C) composite has been undertaken by lock-in thermography. A dedicated 3-D thermal modeling has been introduced, and an efficient numerical algorithm based on finite-difference splitting method in time domain (FDSM-TD) is applied to solve the thermal model. The heat transfer partial differential equation (PDE) and mathematic morphological algorithms are used to filter the phase angle data noise. The diameter of a defect had an appreciable effect on the observed phase angle which consequently has significant implications with regard to estimating the defect depth. Phase angle contrast measurements for a range of defects in a 6.0 mm SiC coated C/C composite specimen indicate that an optimal excitation frequency of 0.525 Hz is available for defect detection. Results obtained with an excitation frequency of 0.525 Hz are used to discuss the limitations of determining the defect size and depth.

This paper describes the quantitative analysis of the boundary, location and depth of subsurface defects by lock-in thermography. The phase difference between defective areas and non-defective areas illustrates the qualitative analysis of the boundary and the location of the subsurface defect. In order to accurately estimate the size, location and depth of the defects, the phase is normalised, the heat transfer partial differential equation (PDE) model is used to filter the noise of normalised phase image and the differential normalised phase profile is employed to determine the boundary and location of the defect. The profile of the differential normalised phase distribution has maximum, minimum and zero points that help to quantitatively determine the boundary and location of the subsurface defect. An artificial neural network (ANN) is proposed to determine the depth of the subsurface defect. Experimental results for a steel plate, a carbon fibre-reinforced polymer (CFRP) sheet–foam sandwich, and honeycomb structure composites with artificial subsurface defects show good agreement with the actual values.

A novel non-destructive ultrasound infrared lock-in thermography (ULT) testing method was presented in order to detect metal specimens with subsurface contacting interfacial defects. An experimental platform was built. Experiments had been carried out to Q235 plates with different testing parameters. The testing effect of amplitude and phase images was analyzed, and the relation between amplitude difference, phase difference, signal-to-noise ratio and modulation frequency was discussed. An adaptive neuro-fuzzy inference system model was built to forecast the depth of defects.

PurposeGreen machining is becoming increasingly more popular due to concern regarding the safety of the environment and human health. The important implementation of stricter Environmental Protection Agency regulations associated with the use of ample amount of coolants and lubricants has led to this study on a new green machining technology with application of water vapor as coolants and lubricants in cutting Ni‐based superalloys and titanium alloy Ti‐6Al‐4V with uncoated carbide inserts (ISO Type K10). The purpose of this paper is to show that machining technology with application of water vapour could be an economical and environmentally compatible lubrication technique for machining difficult‐cut‐materials.Design/methodology/approachIn this paper, the effect of water vapor applications in machining difficult‐cut‐materials have been investigated in detail, the cutting force, the chip deformation coefficient, the rake face wear and the width of tool flank land VB have been examined and analyzed, and a new green cutting technology is researched to machining Ni base superalloys and Ti‐6Al‐4V difficult‐cut‐materials.FindingsThe cutting force of machining Ni base superalloys and Ti‐6Al‐4V was affected by direct water vapor application, being lower than dry cutting and wet machining for all machining conditions; the Λh is the smallest with applications of water vapor as coolants and lubricants compared to dry cutting, pure water and oil water emulsion conditions the tool life extended by about six times than dry cutting, about four times than oil water emulsions at low cutting speed (νcνc>100 m/min) during machining Ti‐6Al‐4V with application of water vapor direct into the cutting zone.Originality/valueThe green cutting technology which applies water vapor as coolants and lubricants advocates a new method for machining difficult‐cut‐materials (Ni base superalloys and Ti‐6Al‐4V) without any environment pollution and operator health problem because the cutting force and chip deformation coefficient are reduced, the tool life is extended, and the tool flank wear can be decreased with applications of water vapor as coolants and lubricants to alleviate the adhering and diffusion wear compared to wet cutting and dry cutting.

Water vapor is a new type of environmental friendly coolant and lubricant. In this study, the friction test was carried out by using the water vapor as lubricant, and the friction pair was made of cement carbide K20 and ANSI 304 stainless steel. In order to study the lubricating action of water vapor as coolant and lubricant in cutting ANSI 304 stainless steel, experiments were carried out with K20 cutter. Through chemical state analyses of elements on tool–chip interface by means of XPS and Gibbs free energy calculation, the chemical reaction process was discussed between water molecule, oxygen atom and fresh tool–chip interface. Experimental results showed that an adsorption film and a tribo-chemical reaction film are formed on the tool–chip surfaces due to its excellent penetration performance and ability to form boundary lubrication layer. The multi-dimensional metal-oxide formed during the reaction weaken the mutual action between tool bulk material and chip. The cutting force and tool flank wear are reduced rapidly, and hence the tool wear is reduced about 50–75% compared with dry machining.

PurposeAt the present time, green cutting has become the focus of attention in ecological and environmental protection. Water vapor is cheap, pollution‐free and eco‐friendly. Therefore, it is a good and economical coolant and lubricant. To find the discipline of nozzle diameter, the parameters of water vapor jet flow and cooling distance influence on its lubricating action effect, experiments were carried out in which YT15 (P10 type in ISO) tool was used in cutting C45 steel.Design/methodology/approachThe vapor generator and vapor feed system are manufactured. The temperature and velocity distribution of water vapor jet flow influences the velocity such that water vapor fills up the capillaries and forms the boundary lubricating film layer in the cutting zone, and the temperature and velocity distribution of the vapor jet flow section contains the effective area for the lubricating effect. Through the temperature distribution measured, the empirical formula of temperature distribution is obtained and simulated by Matlab. The turning experiment was carried out according to quantity in cutting υc=45, 60, 75, 90, 105, 120 mm/min, f=0.1 ∼ 0.3 mm/rev, ap=1, 2, 3, 3.5 mm and the jet flow parameters were changed, respectively.FindingsIt was found that: significant decrease of cutting force can be realized with reduced nozzle diameter, increased the sett pressure and shortened the cooling distance. However, reduced to a certain extent it will lead to the increase of the cutting force. The optimal nozzle diameter is 2 mm for the best lubricating effect. The effect on cutting force of the cooling distance is much better than the setting pressure. Significant decrease of friction coefficient of tool‐chip can be realized with reduced nozzle diameter. However, reduced to a certain extent it will lead to the increase of friction coefficient. Significant thinness of chips can be realized by reducing nozzle diameter. But if the diameter is reduced to a certain degree, chips will be thickened. Increased set pressure and shortened cooling distance can both reduce chip thickness, resulting in reduction of chip deformation coefficient. Since water vapor has the advantage of being cheap, pollution‐free and harmless, and there is no need for disposal and recycling, it is ideal for cooling and lubricating technology in green cutting.Originality/valueThe paper establishes the discipline of nozzle diameter, the parameters of water vapor jet flow and cooling distance influence on its lubricating action effect.

In this letter, a nonlinear photothermal characteristic of dental tissues has been verified by photothermal radiometry at a given frequency with changing of the laser intensity. Subsequently, the high-frequency heterodyne lock-in thermography (HeLIT) scheme has been introduced to overcome shortages of the low infrared camera frame rate and the poor signal-noise ratio. The smooth surface tooth was artificially demineralized at a different time, and then it was detected by HeLIT, Results illustrated that the phase delay increases with the extension of the demineralized treatment time. The comparison experiments between HeLIT and the homodyne lock-in thermography for detecting artificial caries were carried out. Experimental results illustrated that the HeLIT has the merits of high sensitivity and specificity in detecting early caries.

Inspection of aerospace components has always been a challenge. Lock-in thermography is an active technique which is popularly being used for the nondestructive evaluation of subsurface defects in composite materials such as carbon-fiber-reinforced-polymer (CFRP) in aircraft structures. CFRP-foam layered structure composite is often used for anti-heat and adiabatic material in aerospace components. In this paper, a finite element analysis (FEA) of 3D heat conduction is developed in order to investigate the behavior of thermal waves in the CFRP-foam layered structure plates with finite thickness under convective and radiate conditions. The FEA simulation is then utilized to predict the magnitude and phase differences produced by CFRP face-sheet subsurface defects to obtain the optimum inspection parameters. The simulation results are compared with the experimental data. The use of optimum inspection parameters of lock-in thermography to detect PVC modeling defects of CFRP-foam layered structure is also presented in this paper.

A space monocrystalline silicon (c-Si) solar cell under low-energy (< 1 MeV) electron irradiation was investigated using noncontact photocarrier radiometry (PCR). Monte Carlo simulation (MCS) was employed to characterize the effect of different energy electron irradiation on the c-Si solar cell. The carrier transport parameters (carrier lifetime, diffusion coefficient, and surface recombination velocities) were obtained by best fitting the experimental results with a theoretical one-dimensional two-layer PCR model. The results showed that the increase of the irradiation electron energy caused a large reduction of the carrier lifetime and diffusion length. Furthermore, the rear surface recombination velocity of the Si:p base of the solar cell at the irradiation electron energy of 1 MeV was dramatically enhanced due to 1 MeV electron passing through the whole cell. Short-circuit current (Isc) degradation evaluated by PCR was in good agreement with that obtained by electrical measurement.

In this paper, the modulated laser-induced excess minority carrier density wave (CDW) of bipolar semiconductor is developed. An analytical expression of CDW in frequency domain is introduced. The numerical simulations are carried out to analyze the effects of minority carrier transport parameters (minority carrier lifetime, diffusion coefficient, and two surfaces recombination velocities) on response of laser-induced photocarrier radiometry (PCR) signal to frequency for semiconductor silicon wafer. The PCR amplitude increases with increasing the minority carrier lifetime, and decreased with increasing the carrier diffusion coefficient and surface recombination velocity. In contrast, the PCR phase lag decreases with increasing the minority carrier lifetime, and increases with increasing the carrier diffusion coefficient and surface recombination velocity. The silicon (Si) wafer with an artificial defect (mechanical scratch) on the surface is experimentally investigated by PCR scanning image system. The distribution maps of the minority carrier transport parameters are obtained by best-fitting method which is based on the carrier density wave analytical expression, and the influences of the artificial defect on carrier transport parameters are discussed in detail. The experimental results indicate that the surface recombination velocity and carrier diffusivity at artificial damaged location are dramatically increased compared with those in the healthy region. The carrier bulk lifetime of whole Si wafer is obtained to be about 38.33 μs by PCR scanning image measurements. Simultaneously, quasi steady-state photoconductance (QSSPC) method is used to measure the carrier effective lifetime of Si wafer, and it is about 33.85 μs. Therefore, the carrier bulk lifetime of Si wafer by PCR scanning image measurement is in good agreement with the QSSPC measurement. However, QSSPC measurement could obtain only the carrier effective lifetime of Si wafer. Furthermore, PCR scanning image measurement can be employed to measure the carrier transport parameters with high resolution in comparison with QSSPC measurement, and to evaluate the localized imperfection.

The photon-density wave is generated in tooth tissue due to the scattering induced by modulated laser beams, and furthermore, thermal-wave will form because of photothermal effect. A one-dimensional thermal-wave model for three-layer tooth tissue using modulated laser stimulation is developed based on 1D diffusion approximation of the radiative transfer theory in combination with 1D heat conduction equation. Effects of photothermal properties (i.e. light absorption coefficient, scattering coefficient and thermal diffusivity coefficient), enamel depth and caries depth on the photothermal radiometry (PTR) dynamic responses are investigated based on the 1D thermal wave model coupling with photon-density wave. The PTR amplitude and phase delay (the phase difference between the PTR signal and reference signal) are strongly dependent on the photothermal parameters of the dental enamel caries layers (DECLs). PTR amplitude and phase delay increase with increasing DECL absorption coefficient, scattering coefficient and thermal diffusivity. Additionally, PTR amplitude may also increase due to the larger thickness of caries layer, and the PTR phase peak value is generated at low frequencies. The inhomogeneous photothermal properties of dental enamel healthy layer (DEHL) also have obviously influenced PTR amplitude and phase. Increasing DEHL scattering coefficient leads to the increase of PTR amplitude, but has no apparent effect on the PTR phase. While the PTR phase delay increases with increasing DEHL absorption coefficient. The delay of PTR amplitude and phase is enlarged at the high value of DEHL thermal diffusivity. However, the DEHL layer thickness has no apparent effect on the PTR amplitude and phase.The PTR signal of tooth tissue induced by the 808 nm diode laser is monitored using an infrared detector (HgCdTe, spectral width 2.012.0 m), and the PTR amplitude and phase response are obtained using lock-in amplifier (SR830). Through frequency-scanning experiments of dental tissue, PTR dynamic responses can be measured and employed to characterize the inhomogeneity and caries of the tooth tissue. The photothermal parameters and caries characteristic of the tooth issue can be simultaneously obtained by multi-parameters statistic best-fit.Simulation and experimental results show that the PTR dynamic response has the advantages of high sensitivity and high contrast for inhomogeneity and caries of the tooth tissue.

An analytic mathematical model of modulated laser-induced minority carrier density wave of silicon solar cells is developed, and light-induced carrier recombination radiation luminescence method (photocarrier radiometry (PCR)) is employed to detect the doping concentration, impedance and carrier transport parameters. The double knee characteristics of frequency domain response curve are investigated, and in a small ac signal case, the equivalent circuit topology structure of a solar cell is constructed. Through simulation analysis based on minority carrier density wave mathematical model, the effects of doping concentration, resistance and carrier transport parameters on the PCR frequency domain response are investigated. Donor/acceptor concentration, shunt resistance and carrier transport parameters of Si solar cell are obtained by PCR frequency-scanning experiments and multi-parameter fitting. The results show that the first knee position of PCR-detected large-area solar-cell frequency domain response curve is determined by the capacitive effect. The simplified mathematical model can be used to quantitatively describe and determine the doping concentration, shunt resistance and carrier transport parameters of silicon solar cell.