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Cold spray is an attractive and rapidly developing process for additive manufacturing with high efficiency and precision, repairing and coating, especially in aircraft and aerospace applications. Cold spray additive manufacturing deposits micro-particles with large plastic deformation below their melting point, eliminating heat effect zone which could deteriorate the quality of repairing zone. The particle deposition in cold spray is a complex process which involves high strain rate, high contact pressure and high temperature. Here we develop, utilize and validate a thermo-mechanical model to provide a definitive way to predict deposition mechanics and surface deformation evolution for particle deposition process in cold spray additive manufacturing. Both a single particle and dual particles models were developed to investigate the contact interaction between particle/substrate and particle/particle. Different combinations of particle/substrate materials (Cu/Cu, Al/Al, steel/steel, and nickel/nickel) and process parameters were considered in this study. The experimental study was conducted to validate simulation results, providing useful information for understanding the limitations and challenges associated with cold spray additive manufacturing. The framework provides insights into improving the quality and precision of stress/strain formation, particle interactions and particle deposition in cold spray additive manufacturing process.

Up to now, micro milling has been recognized as the most promising technique to mitigate the surface damage of large-aperture KDP crystal used in laser fusion facility. However, there are quantities of damages on the surface of large-aperture KDP crystal to be mitigated. Furthermore, the efficiency and accuracy of manual tool setting is relatively low, and it is easy to damage KDP crystal surface due to mis-operation. Therefore, an automatic tool setting technology for KDP crystal surface damage mitigation based on machine vision is proposed in this research. The automatic tool setting includes fast pre tool setting achieved by image ranging and final tool setting achieved by micro-chip detection. In the process of fast pre tool setting, real-time image of the micro milling cutter is obtained, and the distance between the tool tip and the KDP crystal surface is obtained by image ranging. Finally, the tool tip is quickly positioned 20 μm away from the KDP crystal surface. In the process of final tool setting, the micro milling cutter is retreated to a distance of about 50 μm away from the KDP crystal surface before detecting micro-chips. Therefore, the micro-chips covered by the micro milling cutter will be exposed and appear in the view field of microscope, so as to improve the micro-chip recognition rate. The results showed that the total time of automatic tool setting is 130 s, and the accuracy of automatic tool setting is better than 1.359 μm. Compared with manual tool setting, the automatic tool setting based on machine vision proposed in this research improves the safety, efficiency, and accuracy of independently developed mitigation system for KDP crystal surface damage.

As for ultra-precision grinding of difficult-to-process thin-walled complex components with ball-end grinding wheels, interference is easy to occur. According to screw theory and grinding kinematics, a mathematical model is established to investigate the interference and grinding characteristics of the ball-end wheel. The relationship between grinding wheel inclination angle, C axis rotation angle, grinding position angle and grinding wheel wear are analyzed. As the grinding wheel inclination angle increases, the C axis rotatable range decreases and the grinding position angle increases. The grinding position angle and wheel radius wear show a negative correlation with the C axis rotation angle. Therefore, a trajectory planning criteria for increasing grinding speed as much as possible under the premise of avoiding interference is proposed to design the grinding trajectory. Then grinding point distribution on the ball-end wheel is calculated, and the grinding characteristics, grinding speed and maximum undeformed chip thickness, are investigated. Finally, a complex structural component can be ground without interference, and surface roughness and profile accuracy are improved to 40.2 nm and 0.399 μm, compared with 556 nm and 3.427 μm before ultra-precision grinding. The mathematical model can provide theoretical guidance for the analysis of interference and grinding characteristics in complex components grinding to improve its grinding quality.

When a fracturing fluid invades a nanoscale shale pore structure, it will inevitably affect the ad-/desorption behavior of methane adsorbed on a shale pore wall, impacting the overall methane produ...

In this study, the cellular microstructural features in a subgrain size of carbon nanotube (CNT)-reinforced aluminum matrix nanocomposites produced by laser powder bed fusion (LPBF) (a size range between 0.5–1 μm) were quantitatively extracted and calculated from scanning electron microscopy images by applying a cell segmentation method and various image analysis techniques. Over 80 geometric features for each cellular cell were extracted and statistically analyzed using machine learning techniques to explore the structure–property linkages of carbon nanotube reinforced AlSi10Mg nanocomposites. Predictive models for hardness and relative mass density were established using these subgrain cellular microstructural features. Data dimension reduction using principal component analysis was conducted to reduce the feature number to 3. The results showed that even AlSi10Mg nanocomposite specimens produced using different laser parameters exhibited similar Al–Si eutectic microstructures, displaying a large difference in their mechanical properties including hardness and relative mass density due to cellular structure variance. For hardness prediction, the Extra Tress regression models showed a relative error of 2.47% for prediction accuracies. For the relative mass density prediction, the Decision Tress regression models showed a relative error of 1.42% for prediction accuracies. The results demonstrate that the developed models deliver satisfactory performance for hardness and relative mass density prediction of AlSi10Mg nanocomposites. The framework established in this study can be applied to the LPBF process optimization and mechanical properties manipulation of AlSi10Mg-based alloys and other additive manufacturing newly designed alloys or composites.

In this study, transverse heat flow suppression (THFS) technique was proposed to enhance the ability of thermal-wave radar thermography (TWRT) to resist lateral thermal diffusion and uneven heating. The enhanced TWRT was used to detect subsurface defects of carbon fiber reinforced plastic (CFRP) laminates. The principle of THFS was described in detail by the optical flow analogy. The three-dimension (3-D) thermal-wave model stimulated by the uneven linear frequency modulation (LFM) thermal flow was introduced. The thermal-wave signal was processed by several different postprocessing characteristic extraction algorithms [Cross-correlation algorithm (CC), dual-orthogonal demodulation algorithm (DOD), fractional Fourier transform (FrFT), and principal component analysis (PCA)]. The comparison between normalized DOD amplitude/phase and normalized DOD-THFS amplitude/phase was carried out. The simulation results depicted THFS can significantly improve the difference between defect location and nondefect location. Nine CFRP specimens with artificial flat-bottom holes (FBHs) were prepared for nondestructive testing and evaluation (NDT&E) by enhanced TWRT. Seventy-two FBHs were prepared to test the probability of detection (PoD) of the enhanced TWRT. Hit/miss method was used to count defect information. The results demonstrated that the enhanced TWRT can realize the effective detection of defects (90% detection probability) with a diameter depth ratio of 5.06 under 95% confidence level. Compared with two state-of-the-art approaches, the proposed DOD-THFS phase has a better defect detection signal-to-noise ratio (SNR).

In high power laser facility, irreversible damage on fused silica optics, induced by laser irradiation or processing, seriously affects the service life of optics. Therefore, the work of inhibiting damage growth has been carried out in various countries. In our work, an integrated multi-station system is designed to detect and mitigate surface damage on fused silica. The process of processing fused silica optics include UV laser conditioning, surface damage detection and surface damage mitigation with CO2 laser. UV laser conditioning pre-initiates surface damage on fused silica optics with the laser flux less than Laser-Induced Damage Threshold (LIDT). Images of surface damage acquired from camera are processed by improved global threshold segmentation algorithm to extract damage information. Finally, CO2 laser is applied to process the damage with specific morphology to enhance the laser damage resistance. This integrated multi-station system saves the repeated optics installation time between the workstations with the positioning accuracy of 20 μm. Furthermore, the damage with diameter of 10 μm is mitigated to prolong service life of processed fused silica optics. The efficient and accurate integrated multi-station system is of great significance for off-line detecting and mitigating surface damage of fused silica optics in high power laser facility.

Hierarchical structures have attracted considerable interest due to their super-oleophobic/super-hydrophobic behavior. However, it is rare to present a novel additive manufacturing (AM) approach to fabricate hierarchical metal structures (HMSs). A micro/nano mixture ink was deposited on a substrate and a laser was used to selectively scan the ink layer. A new layer of ink was deposited on the previous consolidation layer during manufacturing. The surfaces of the as-sintered HMSs exhibit inherently super-hydrophilic and super-oleophobic behavior with a 155° contact angle (CA) with oil. Furthermore, the HMSs were successfully turned into super-hydrophobic and super-oleophilic mode (with a 152° CA) after surface modification with a solvent-free, electrostatic polytetrafluoroethylene particle deposition. They can be used as oil/water separation media by the functional surfaces existing in the pore channels. The experimental study of HMSs shows an effective removal of oil contaminants from water. The developed process also possesses an advantage of AM of HMSs with complex shapes in ambient air under the protection of an organic ink. Importantly, the present approach could be extended to a vast number of HMSs, for the preparation of highly durable functional materials for various applications.

Micro-optics and micro-structures play important roles in the field of optics. A multi-step processing strategy with the combination of various processing technologies has been applied to fabricate micro-optics and micro-structures. However, the multi-step processing method is complex and expensive. In this work, a rapid CO2 laser processing technique is proposed to fabricate micro-optics and micro-structures on fused silica materials. First, high-power and short-pulse CO2 laser is used to achieve rapid prototyping of micro-optics and micro-structures with pre-designed geometry on fused silica. In this step, a maximum material removal rate of 1.53 mm3/min could be achieved with surface roughness better than 100 nm. Then, using the same CO2 laser source with reduced laser power density, the initially processed fused silica surface could be smoothed to improve the surface quality. By simulating the CO2 laser interaction with fused silica material, the formation mechanism of smooth surface is revealed, and the processing parameters for achieving smooth silica surface are proposed. The surface roughness of finally processed silica surface could reach 10.8 nm. Finally, as an application example of the processed two-step CO2 laser processing method, a micro-structure with special hexagonal shape on fused silica optics is successfully processed. The proposed rapid CO2 laser processing technique for the fabrication of micro-optics and micro-structures on fused silica materials can be realized with only one equipment, which can not only ensure the processing accuracy and efficiency but also reduce the processing cost.

Brittle KH2PO4 (KDP) crystal is difficult-to-machine because of its low fracture resistance whereby brittle cracks can be easily introduced in machining processes. To achieve ductile machining without any cracks, this type of materials is generally processed by some ultra-precision machining techniques at ambient temperature with nanoscale material removal, yielding low machining efficiency and high processing cost. Recently, thermal-assisted techniques have been used to successfully facilitate the machining of some difficult-to-machine materials, like superalloys, but little effort has been made to explore whether the temperature effect can contribute to the ductile machinability of brittle materials yet. Thus, the aim of this study is to figure out the specific role of temperature in the deformation behaviours of brittle KDP crystal by nano indentation/scratch methods. It is found that compared with those at ambient temperature (AT, i.e. 23 °C), the hardness and Elastic modulus of KDP crystal at elevated temperature (ET, i.e. 160 °C) decrease substantially by 21.4% and 32.5%, respectively, while the fracture toughness increases greatly by 15.5%, implying a higher ability of ductile deformation at ET. Meanwhile, the scratch length within ductile removal has been identified to be extended more than 4 times by increasing temperature from AT to ET. Both the quantity and size of brittle features (e.g., cracks and chunk removal) show a reducing trend with the increase of temperature. To uncover the underlying mechanism of this phenomenon, an updated stress field model is proposed to analyze the scratch-induced stress distribution by considering the evolution of material property at various temperature. These presented results are significant for the future design of specific thermal-assisted processing techniques for machining brittle materials efficiently.

Potassium dihydrogen phosphate (KDP) crystal has been regarded as the solely irreplaceable component in laser-driven inertial confinement fusion (ICF) facilities. Nevertheless, the laser-induced damage on KDP crystal surfaces under highenergy laser irradiation considerably restricts the output power of ICF facilities. The laser damage event on KDP surface is an extremely complex process, among which the non-heat initial energy deposition is regarded as the major absorbed energy source, determining the subsequent thermal damage process and final damage morphology. The initial energy deposition process is a non-heat stage, where the plasmas are generated from ionization processes under intense laser irradiation. However, there is still no available model that can well reproduce the dynamic interaction behaviors between the high-energy laser and plasmas in the initial energy deposition process, resulting in the laser-induced damage mechanisms on KDP crystal surface still not fully revealed. In this work, a Particle-In-Cell (PIC) model is established to investigate the initial dynamic damage behaviors of KDP crystals under intense laser irradiation. On basis of this model, the crater formation process and the particle ejection dynamics involved in the laser damage event are reproduced. The reproduced characteristic parameters of laser damage craters on KDP input and output surfaces, and the obtained particle ejection angles are consistent with the previously reported laser damage morphology, which verifies the effectiveness of the established PIC model. This work could provide theoretical means for investigating the initial energy deposition process and also offer further insights in understanding the laser-induced damage mechanisms of KDP crystal components.

The issue of laser-induced damage of transparent dielectric optics has severely limited the development of high-power laser systems. Exploring the transient dynamic behaviors of laser damage on KDP surface by developing multi-physics coupling dynamics model is an important way to reveal the mechanism of nanosecond laser damage. In this work, KDP crystals are taken as an example to explore the mechanism of laser-induced surface damage. Based on the theories of electromagnetic field, heat conduction and fluid dynamics, a multi-physics coupling dynamics model is established for describing the evolution of nanosecond damage processes. The dynamics of laser energy transmission, thermal field distribution and damage morphology during nanosecond laser irradiation are simulated with this model. It is found that the enhancement of light intensity caused by surface defect plays an important role in the initial energy deposition and damage initiation of the laser irradiation area. The evolution of temperature field and crater morphology during subsequent laser irradiation is helpful to understand the laser damage process. The feasibility of this model is verified by the morphology information of typical defect-induced laser damage. This work provides further insights in explaining the laser-induced damage by surface defects on KDP crystals. The model can be also applied to investigate the laser damage mechanisms of other transparent dielectric optics.

For quantum-dot light-emitting diodes (QD-LED), replacing Cd-based II-VI nanocrystals (NCs) with the Cu-In-Zn-VI counterparts combines the consideration of environmental benignity and device performance. To prove this concept, the chemical composition and nanostructures of Cu-In-Zn-VI nanocrystals need to be thoroughly explored aiming to competitive optoelectronic properties. Herein, we reported a detailed study of Cu–In–Zn–Se–S synthesis and demonstrated how the optical bandgap, emission full width at half-maximum (FWHM) and the performance of QD-LED were tuned by simply changing the dose of precursors in a non-injection synthesis. Evident by optical absorption, the optimization of Se and Cu doses enabled good dispersity and desired emission wavelength. Further analysis of photo-electron spectroscopy revealed the chemical composition from core to surface favored soft confinement of exciton by gradually increasing the loading of Zn element. Finally, we successfully demonstrated solution-processed QD-LEDs with the best external quantum efficiencies as high as 4.2% and emission wavelength centering at 663 nm. To our best knowledge, this is the most efficient solution-processed red QD-LED based on Cu-In-Zn-VI nanocrystals.

A novel magnetorheological finishing (MRF) process using a small ball-end permanent-magnet polishing head is proposed, and a four-axes linkage dedicated MRF machine tool is fabricated to achieve the nanofinishing of an irregular ψ-shaped small-bore complex component with concave surfaces of a curvature radius less than 3 mm. The processing method of the complex component is introduced. Magnetostatic simulation during the entire finishing path is carried out to analyze the material removal characteristics. A typical ψ-shaped small-bore complex component is polished on the developed device, and a fine surface quality is obtained with surface roughness Ra of 0.0107 μm and surface accuracy of the finished spherical surfaces of 0.3320 μm (PV). These findings indicate that the proposed MRF process can perform the nanofinishing of a kind of small-bore complex component with small-curvature-radius concave surfaces. Keywords: Complex component, Magnetorheological finishing, Magnetostatic simulation, Small curvature radius

The adherent behaviors of hydroxyl-terminated polybutadiene (HTPB), a typical high viscosity liquid widely used as a binder in rocket motor propellants, onto the copper (Cu) surfaces with/without the interference of Al nanoparticles were investigated by classical molecular dynamics (MD) simulations. The results indicate that HTPB molecules adsorbed directly onto Cu(001) surface exhibit the tendency to distribute parallel to the 〈110〉 crystal direction family as a result of tense atom arrangement along the close-packed crystal directions. The dynamic hydrogen-bonded network, formed by inter-/intra-molecular interactions among neighbouring hydroxyl groups, is also suggested to exert strong influence on the distribution of HTPB molecules. Moreover, Al nanoparticles have been proved to be readily enveloped by HTPB chains when placed close to the pure high viscosity liquid, which will in turn restrict the mobility of HTPB molecules, eventually resulting in the decrease of wettability of HTPB droplet on Cu surface. The flow slip behavior of HTPB liquid on Cu surface, regardless of the presence of Al nanoparticles, was tested and directly compared by confined shear simulations. The Al hemispheres, acting as convex obstacles on the flat surface, seem to be capable of suppressing the slippage of chain-like HTPB molecules, which will be easily entangled by local protrusions. Therefore, it can be inferred that the flow behavior and interfacial wettability of high viscosity liquid will be largely influenced by the discontinuous solid-phase particles dispersed in it.

Methane diffusion plays an essential role in shale gas production, linking gas desorption and seepage. Accurate measurement of the methane diffusion coefficient is a key factor for evaluating the potential for multi-gas transport behavior in shales. Thus, a pressure pulse experiment was carried out in this work, the multiscale mass transfer process of methane was simulated, and the mechanism of pore pressure effect on the diffusion ability of shale gas was revealed. The experimental results indicate that the diffusion of methane can be divided into three stages based on the relationship between pressure and time, in which different pore diameters correspond to different diffusion mechanisms. In Stage I, free molecule diffusion is dominant; in Stage II, diffusion occurs through relatively large pores as a result of the combined action of Knudsen diffusion and surface diffusion in those pores; in Stage III, it is attributed to internal configurational diffusion in organic-matter pores. A higher pore pressure increases methane adsorption capacity, and multilayers adsorption of methane on the pore surface reduces the pore sizes. The Knudsen diffusion rate then decreases and the configurational diffusion rate increases. Therefore, as pore pressure increases, the diffusion coefficient of large particles in Stage II decreases, while that in Stage III increases. It is shown that the multiscale mass transfer of shale gas with pore pressure can be effectively simulated through the pressure pulse method proposed in this paper. The method additionally allows the shale formation temperature and overburden pressure to be reliably simulated. This work provides an important workflow for the investigation of gas multiscale transport behavior in shales.

As a rapid and efficient processing technology, CO2 laser processing has been applied to remove fused silica materials. However, thermal effect caused by CO2 laser would lead to thermal modification layer, thermal deformation and residual stress in processed fused silica optics. To reduce the thermal effect, high power and short pulse CO2 laser is applied to remove the surface material of fused silica. In this work, a model coupling the physical processes of heat transfer and phase transition was established to simulate the complex interaction of CO2 laser with fused silica. Then, the model was applied to investigate the evolutions of temperature distribution and surface morphology involved in the laser ablating and melting processes. The results indicate that with the increase of laser power and decrease of pulse width, positive effect would take place that the radius-depth ratio of ablating area increases and the heat-affected area becomes smaller. For the application of CO2 laser with 0.2 μs pulse width and 800 kW peak power, fused silica material would quickly reach the ablation state. The ablation depth is less than 1 μm, and the thickness of heat-affected area is about 80 nm. It means that the high power and short pulse CO2 laser is equivalent to a hot grinding ball head, which can remove the material rapidly with small heat-affected area on fused silica surface. The simulation results of line scanning processing with CO2 laser were finally compared with the experiment ones, which verified the feasibility of the established model. The suggestions and prospective for improving the model were put forward as well. Keywords: CO2 laser, Fused silica, Heat-affected area, Laser processing

All-solid-state electrochromic devices with the structure of glass/ITO/WO3/Ta2O5/Li/V2O5/ITO were prepared by an evaporation method. Because of the use of a V2O5 complementary layer, the ECD can achieve obvious color change between yellow-green and emerald green with superior cycling performance up to 5000 cycles, indicating the great potential in smart window applications.

Nanosecond laser-induced damage on (potassium dihydrogen phosphate) KDP crystals is a complex process, which involves coupled actions of multi-physics fields. However, the mechanisms governing the laser damage behaviors have not been fully understood and there have been no available models to accurately describe this complex process. In this work, based on the theories of electromagnetic, thermodynamic, and hydrodynamic fields, a coupled multi-physics model is developed to describe the transient behavior of laser-supported energy deposition and diffusion accompanied by the surface defect (e.g., surface cracks)-initiated laser damage process. It is found that the light intensification caused by the defects near the crystal surface plays a significant role in triggering the laser-induced damage, and a large amount of energy is quickly deposited via the light intensity-activated nonlinear excitation. Using the developed model, the maximum temperature of the crystal material irradiated by a 3 ns pulse laser is calculated, which agrees well with previously reported experimental results. Furthermore, the modeling results suggest that physical processes such as material melting, boiling, and flowing have effects on the evolution of the laser damage process. In addition, the experimentally measured morphology of laser damage sites exhibits damage features of boiling cores, molten regions, and fracture zones, which are direct evidence of bowl-shaped high-temperature expansion predicted by the model. These results well validate that the proposed coupled multi-physics model is competent to describe the dynamic behaviors of laser damage, which can serve as a powerful tool to understand the general mechanisms of laser interactions with KDP optical crystals in the presence of different defects.

A series of D–A-type copolymers was designed and studied systematically for the purpose of gaining a deeper understanding of how the D/A ratio may influence the geometric and electronic properties when it varies from 2:1 to 6:1 by using DFT method. The results show that it has a significant effect on the bond length alternation, band gap, bandwidth and effective mass of carriers of the designed D–A-type copolymers. But its influence on the geometric and electronic properties shows something very different in degree when it increases from 2:1 to 4:1 and then increases further from 4:1 to 6:1. It is found that the effects of increasing D/A ratio on geometric and electronic properties are much stronger when the D/A ratio increases from 2:1 to 4:1 than when it further increases from 4:1 to 6:1. The theoretical results show that the polymers with a D/A ratio of 2:1 have much smaller effective mass of carriers and much wider bandwidth compared to those polymers with the D/A ratio of 4:1 and 6:1. Therefo...

As-cast polymer solar cells without any additive and pre- or post-treatments principally have high compatibility with mass production technologies, and efforts in achieving higher efficiencies are typically promoted by engineering new donor and acceptor materials. In this study, a binary solvent processing approach using chloroform (CF), as a good low boiling point solvent for both the donor polymer PTQ10 and the non-fullerene acceptor IT-4Cl, and mesitylene (MES), as a semi-orthogonal co-solvent with relatively high boiling point and weak solubility to the acceptor, is explored. Due to the selective orthogonality of MES to the IT-4Cl acceptor, an optimized morphology has been realized for the as-cast device based on the PTQ10:IT-4Cl blend, which leads to a simultaneous improvement in the open-circuit voltage, short-circuit current, and fill factor, finally achieving a high as-cast efficiency of over 13%. Furthermore, the as-cast devices fabricated with this binary solvent system exhibit good air stability and great accessibility in large area cells. Our findings provide an alternative guideline for the optimization of as-cast polymer solar cells.

Localized CO2 laser repairing of surface damage on fused silica optics has been successfully applied in high-power laser system in the field of controllable nuclear fusion. In order to accurately predict the surface topography evolution and to reveal the intrinsic physical mechanism during the process of laser mitigation, experiments of localized CO2 laser mitigation were firstly carried out to analyze the features of mitigated craters under different laser powers. Then a multi-physics coupled mathematical model was developed based on the fluid control equation, heat and mass transfer equation and material phase transition kinetics to investigate the thermodynamic and kinetic behaviors of laser interaction with silica. The model considered the effects of Marangoni convection, gravity, capillary force and vaporization recoil pressure, as well as the nonlinear variation of physical parameters of silica material with respect to temperature. The results showed that with the increase of laser power, the material ablation and the appearance of raised rim occurred simultaneously. The depth of the mitigated crater increased sharply when the threshold for material ablation was attained, while the lateral dimension increased linearly. The vaporization recoil pressure was found to be the dominant factor for the formation of Gaussian crater with the raised rim feature. The capillary force caused the material at the edge of the molten pool to have a tendency to reflow after laser shutting down, but it was too small to change the surface topography. This work could significantly contribute to the understanding of laser mitigation process, which laid the foundation for the accurate prediction and evaluation of surface quality of CO2 laser repaired fused silica surface.

In order to in-depth study the surface morphology formation mechanism and surface quality control methods of fused silica repaired sites, numerical simulation and experimental method were firstly used to analyze the process of CO2 laser rapid ablation mitigation, as well as the relationships between processing parameters, repaired angle and surface quality. Then the physical problems of the heat-affected zone, fictive temperature and structure relaxation under the irradiation of pulsed laser were studied through the mathematical model and Raman spectroscopy system. The studies found that the fixed depth morphology was formed starting from the third track’s laser scanning during the processing of fused silica by the pulsed laser that moved according to the arc trajectory. The bottom of the processed morphology presented uneven concave-convex features, which was different from the uniform topography formed by the laser linear scanning processing. The processing angle decreased as the trajectory indentation increased, while there was no clear variation law between the processed surface quality and the indentation. The thickness of the heat-affected zone characterized by the fictive temperature was consistent with the experiment, and it was proportional to the laser pulse width. The negative factors caused by the thermal effect in the laser repair process could be suppressed by reducing the laser pulse width. These studies can provide guidance for the optimization of the CO2 laser repair process and the improvement of the repaired surface quality.

Micro-milling is the prevailing method to repair laser-induced surface damage on potassium dihydrogen phosphate crystal components applied in high-power laser systems. Scallop tool marks are inevitably generated on repaired surfaces due to the interaction of neighboring tool paths involved in the micro-milling process. In this work, the effect of scallop tool marks on the optical performance of micro-milled crystal surfaces is theoretically and experimentally investigated. The results indicate that surface tool marks could be categorized into four bands having different period lengths (L) according to the levels of induced light intensification: high-frequency (0.1 μm ≤ L ≤ 0.7 μm), high-risk (0.7 μm ≤ L ≤ 1.2 μm), intermediate-frequency (1.2 μm ≤ L ≤ 100 μm), and low-frequency (100 μm ≤ L ≤ 1000 μm) bands. Tool marks in high-risk band play dominant role in degrading the repairing effectiveness that they should be strictly excluded. While for intermediate-frequency band marks, the induced light intensification is low, and the laser damage resistance and transmittance capacity are comparable to those of tool mark-free surface. The experimental results agree well with simulation results, which suggest that machining parameters corresponding to tool marks in intermediate-frequency band should be preferred in the actual micro-milling repairing process. Keywords: Potassium dihydrogen phosphate crystal, Surface damage repairing, Micro-milling, Periodic tool marks, Laser damage resistance, Light intensity distribution

Micro-milling has been considered as the most promising method to repair the micro-defects on the surface of KH2PO4 (KDP) crystal. However, acquiring an ultra-smooth repaired surface by ball-end milling remains a longstanding challenge for KDP crystal due to its soft-brittle properties. In micro ball-end milling of KDP crystal, tool inclination angle has a remarkable effect on the quality of machined surface. Therefore, picking out an optimal tool inclination angle plays a great role in guaranteeing the ductile-mode machining and improving the surface quality of brittle KDP crystal. In this work, the effect of tool inclination on the brittle–ductile transition and surface quality of micro-milled KDP crystal were investigated. A theoretical model considering the tool inclination direction and angle was proposed to calculate the undeformed chip thickness (UCT) and cutting speed involved in the micro ball-end milling process. Besides, micro groove experiments were conducted to evaluate the change rule of the brittle–ductile transition and surface quality related to the tool inclination. The experimental results agree well with the theoretical results, which shows that the evolution of surface quality with respect to the tool inclination depends on the competitive mechanisms between UCT and cutting speed. Inclining the cutter in the tool feed direction (positive inclination angle) and increasing the tool inclination angle both contribute to the ductile cutting of KDP crystal. A + 45° inclination angle is the optimal angle for the micro ball-end milling of KDP crystal and the best surface roughness value achieved could be up to 35.3 nm.

Adsorbed gas is a significant component of shale gas due to the abundant nanopores of organic matter in shales. Methane adsorption behavior on shale matrix is complex considering the geochemical properties, lithology, pore structure and pressure-temperature conditions. In this work, methane adsorption experiments were conducted through a gravimetric method for shale samples at reservoir pressure and temperature conditions. Meanwhile, total organic carbon (TOC), mineral contents and pore structure parameters of samples were measured, respectively. Experimental results show that (1) an excess adsorption phenomenon is obvious at high-pressure and high-temperature conditions; (2)methane adsorption capacity of shale tends to increase with an increase of TOC; (3) lithology and pore structure also affect the methane adsorption capacity of shales, inducing the different adsorption results of two samples with similar TOC; (4) a shale with a large TOC, a low illite content, a large specific area, a large pore volume and a small average diameter would have a strong methane adsorption capacity, nevertheless the effect of TOC is generally dominant. In order to further investigate the methane adsorption behavior on shales, a simplified local density adsorption model considering the cylindrical pore geometry is established, and is regressed and verified by the experimental data. The modeling results indicate that a sample with a large TOC would have a strong fluid-solid interaction energy and a large surface area of methane adsorption. At last, the mechanism of methane adsorption on shales at in-situ conditions is summarized. This work is beneficial for an accurate shale gas reservoir modeling.

Multiscale mass transport behavior is obvious during shale gas development. Considering multiscale pore structure, multiple gas transport mechanisms and multiple micro effects, a unified mathematical model of shale equivalent permeability was constructed. Then the characteristics of shale permeability during a real production process was analyzed. The main impacts of multiscale mass transport of shale gas was investigated, including gas-solid properties, pore geometry and its connectivity, and temperature and pressure conditions. An evaluation index of multiscale mass transport behavior of shale gas was then put forward, which was the proportion of pores with diameter between 50 and 200 nm. A specific methodology on evaluating multiscale mass transport of shale gas was presented based on mesoscience. Considering the main problems in shale gas development, the coordination mechanisms for multiscale mass transport processes was put forward, which includes controlling water phase trapping damage, enlarging and connecting nanopores in matrix, and accelerating gas desorption-diffusion.

In this paper, a new depth-resolved tomography approach titled laser induced chirp-pulsed radar photothermal tomography (CR-PT) is introduced, and it is employed for the 3D visualization detection for carbon fiber reinforced polymer (CFRP). Initially, the time delay correlation dual orthogonal demodulation (DOD) algorithm is applied to extract the time/frequency-domain characteristic sequence of the chirp-pulsed radar signal, and the applicability of CR-PT is analyzed by COMSOL simulation environment. Subsequently, the correctness of the simulation analysis is verified by the experiment of detecting CFRP with the flat bottom holes by CR-PT. Meanwhile, the accuracy of the shape, position, and depth of the defects detected by CR-PT is determined. Finally, the immersion ultrasonic C-scan imaging and CR-PT are employed to compare and analyze the delamination defect of CFRP composites, which proved the superiority of CR-PT. The experimental results illustrated that CR-PT technique can achieve high-quality 3D geometric reconstruction of CFRP delamination defect, which provides a new attempt and method for quantitative non-destructive evaluation and tomography of CFRP composites.

We demonstrated the multimodal optical excitation pulsed thermography, and this technique can enhance the defect detectability and the depth-resolution dynamic range for the propellant /cladding layer interface debonding defects of the solid propellant rocket motor. Firstly, three-dimensional (3D) thermal-wave model which stimulated by a pulse excitation thermal source was built. The temperature field distribution and the thermal-wave diffusion behavior were analyzed. Subsequently, multiple feature extraction algorithms were proposed and applied to extract characteristic images. The experimental set-up was developed and utilized to detect cladding layers with artificial defects. The results demonstrate that pulse thermography optimized by PLSR and ICA can achieve better detection of interface debonding defects. The characteristic profiles were analyzed to evaluate the ability of feature images to characterize the defect diameter and depth. The results depict that the 1st independent component has a better detection effect for defect depth and diameter.

A flexible reflective-type electrochromic device based on PB films has been constructed. Based on the subtractive color-mixing theory, the demonstrated electrochromic device exhibits a unique reversible color changes from leaf-green to sand-yellow by electrochemical operation. Fast response time of 0.9 s for bleaching and 1.3 s for coloring is observed, which is faster than most reports. In addition, the device exhibits high electrochromic stability of more than 100 cycles without compromising its performance. The flexible device shows promise for a broad range of potential application in the wearable electrochromic displays and camouflage.

Dental caries is a worldwide disease, which will cause adverse effects if it is not treated in time. To accurate detect the early caries, a dental caries recognized approach based on infrared thermal diffusion, titled thermal-wave radar imaging (TWRI) technique was utilized to detect dental caries at an early stage in this present study. One-dimensional (1D) thermal-wave model under linear frequency modulation (or -chirp) thermal flux was built and analyzed the chirp thermal-wave diffusion behavior. In addition, simulated caries environment in vitro was designed and proposed for the treatment of artificial dental caries. Four intact tooth tissues were demineralized with this etching agent for different time on the dental occlusal surface. For the safety of the laser application in clinical trials, the relationship between laser power intensity and dental surface temperature rise has been investigated. When the laser power intensity was controlled within 23.3W under the irradiation area is 2mm×2mm, the surface temperature rise of dental specimen can be dominated within 5℃. The comparison experiment between TWRI and lock-in thermography was investigated, and TWRI phase represents a high signal-to noise ratio to the early caries. μCT was utilized to 3D tomography for the dental specimen to obtain the actual caries inside the specimen. The experimental results illustrated that TWRI approach can be used as an effective method for early caries diagnosis.

The machining-induced cracks and other defects on the surface of fused silica would incur damage when irradiated by intense lasers, which greatly shortens the service life of the fused silica optical components. The high absorption coefficient of fused silica for far-infrared lasers makes it possible to use low-energy CO2 lasers to melt and heal micro defects on the surface, and hence improve its damage threshold under the service conditions of extremely intense laser. However, the air in the cracks may evolve into bubbles during the laser healing process, but the law of crack morphology evolution and the bubble formation mechanism have not been clearly revealed. In this work, a simulation model of the healing process of fused silica surface cracks under the effect of low-energy CO2 laser is established. Three bubble formation mechanisms (i.e., the uneven fluidity caused by temperature gradient, the collapse effect caused by inclined cracks, and the internal cracks) are identified based on the simulation results of cracks with various original morphologies and characteristic structural parameters. The simulated fused silica morphology is consistent with the results of the laser healing experiment. This work can provide theoretical guidance for the optimization of optical manufacturing parameters of fused silica, as well as the CO2 laser healing and polishing strategies.

Micro-milling is a promising approach to repair the micro-defects on the surface of potassium dihydrogen phosphate (KDP) crystal. However, KDP crystal is difficult to machine due to its properties of soft-brittle and easy deliquescence. This study investigates the minimum undeformed chip thickness hm and the size effect in micro end-milling of KDP crystal by comprehensively analyzing cutting force, specific cutting force and machined surface quality. A model of the chip formation, which is capable of connecting the minimum undeformed chip thickness, the undeformed chip thickness and the periodicity of cutting force together, is developed to predict the value of minimum undeformed chip thickness. The normalized minimum undeformed chip thickness λe in terms of the ratio of the minimum undeformed chip thickness to the cutting edge radius re, is estimated to be 0.43 ≤ λe ≤ 0.48. The significantly non-proportional increase of specific cutting force indicates the existence of size effects when the ratio of feed per tooth to cutting edge radius ft/re is less than 0.7. The machined surface quality also reflects severe size effect by the phenomenon that the micro cracks and brittle pits appear on the groove base, and the value of surface roughness Ra is large when the ratio ft/re is less than 0.5. Furthermore, the surface quality deteriorates and the brittle cutting appears when the ratio ft/re is much larger than 1 which seems similar to macro-milling. The perfect machined surface with almost no ploughing effect and brittle cutting is achieved at a ratio ft/re of 0.7. Therefore, a feed per tooth, slightly larger than the minimum undeformed chip thickness but smaller than cutting edge radius, is recommended for micro-milling of KDP crystal or soft-brittle crystal.

Potassium dihydrogen phosphate (KH2PO4 or KDP) crystal is a typical soft-brittle optical crystal, and the size effect and brittle cutting mode are easy to appear in micro ball end-milling of KDP crystal. In this paper, micro-grooving experiments are conducted to study the size effect and brittle cutting in micro ball end-milling of KDP crystal with different feed rate and depth of cut. The cutting force, machined groove base quality and chip morphology are collected and analyzed carefully. The size effect is discovered by the phenomena of the existence of oscillations and relaxations in cutting force and hyper-proportional increase of specific cutting force, when the ratio of feed per tooth to cutting edge radius ft/re is less than 1. While the brittle cutting mode is detected through the existence of sharp fluctuations in cutting force and cracks on the groove base when the ratio ft/re is larger than 2. From the further comprehensive analysis of cutting force, specific cutting force, machined groove base quality and chip morphology, the cutting parameters with ratios of the maximum undeformed chip thickness in one cutting circle to cutting edge radius hmax/re around 0.14, 0.2 and 0.4 are regarded as size effect, optimal and brittle cutting points, respectively. The size effect, ductile cutting and brittle cutting zones are divided by the size effect and brittle cutting boundaries (points). Among the optimal points, the depth of cut of 2 μm with the ratio ft/re of 1 is the optimal cutting parameter for micro ball end-milling of KDP crystal.

To determine whether a potassium dihydrogen phosphate (KDP) surface mitigated by micro-milling would potentially threaten downstream optics, we calculated the light-field modulation based on angular spectrum diffraction theory, and performed a laser damage test on downstream fused silica. The results showed that the downstream light intensification caused by a Gaussian mitigation pit of 800 μm width and 10 μm depth reached a peak value near the KDP rear surface, decreased sharply afterward, and eventually kept stable with the increase in downstream distance. The solved peak value of light intensification exceeded 6 in a range 8–19 mm downstream from the KDP rear surface, which is the most dangerous for downstream optics. Laser damage sites were then induced on the fused silica surface in subsequent laser damage tests. When the distance downstream was greater than 44 mm with a downstream light intensification of less than 3, there were no potential damage threats to downstream optics. The study proves that a mitigated KDP surface can cause laser damage to downstream optical components, to which attention should be paid in an actual application. Through this work, we find that the current manufacturing process and the mitigation index still need to be improved. The research methods and calculation models are also of great reference significance for related studies like optics mitigation and laser damage.

Manufacturing-induced defects have drawn more and more attentions to improve the laser damage resistance performance of KDP crystal applied in high-power laser systems. Here, the morphology of surface scratches on diamond fly-cut KDP crystal is characterized and their effect on the laser damage resistance is theoretically and experimentally investigated. The results indicate that surface scratches could lower laser-induced damage threshold (LIDT) by modulating incident lasers and producing resultant local light intensifications. The induced maximum light intensity enhancement factors (LIEFs) are dependent on scratch shapes and dimensions. The diffraction effects originating from scratch edges are responsible for the strongest light intensification. Even for ultra-precision finished KDP surface with scratches that well satisfy the currently applied scratch/dig specification, the induced LIEFs are quite high, indicating that the actual defect dimension allowance should be amended and specified according to the defect-induced LIEFs. The effect of scratches on laser damage resistance is experimentally verified by the tested LIDT, which is approximately consistent with the simulation one. The morphologies of laser damage sites further confirm the role of scratches in lowering LIDT. This work could offer new perspective and guidance for fully evaluating the performance of ultra-precision manufactured optical materials applied in high-power laser facilities. Keywords: KDP crystal, Manufacturing-induced defects, Diamond fly-cutting, Laser damage resistance performance, Light intensification

To thoroughly disclose the role of the siloxane-terminated side chain with different substituent positions, three difluorobenzotriazole-dithienylbenzodithiophene (FTAZ-BDTT)-based polymers PBZ-1Si, PBZ-2Si, and PBZ-3Si with the siloxane-terminated side chain on the FTAZ unit (PBZ-1Si), on the BDTT unit (PBZ-2Si), and both on BDTT and FTAZ units (PBZ-3Si), respectively, were synthesized. The different side chain substitutions have slight influences on absorption behavior, thermal stability, and frontier molecular orbitals but have shown a great effect on the aggregation of the polymers. Grazing-incidence wide-angle X-ray scattering measurements reveal that, relative to PBZ-1Si with branched alkyl on the BDTT unit, polymers PBZ-2Si and PBZ-3Si, bearing the siloxane-terminated side chains on the BDTT unit, exhibit smaller π-π stacking distances and larger crystal coherence lengths, suggesting that adopting the siloxane-terminated side chain on the BDTT unit can promote the interchain π-π interaction and the ordering of molecular packing. With IT-M as the non-fullerene acceptor, among the three polymers, the PBZ-2Si-based active layer possesses the highest ordered crystals for both polymers and IT-M as well as the purest domain, which affords efficient exciton dissociation, the most balanced hole-electron transport, and reduced recombination, leading to the highest short-circuit current density (

Surface defects introduced by conventional mechanical processing methods can induce irreversible damage and reduce the service life of optics applied in high-power lasers. Compared to mechanical processing, laser polishing with moving beam spot is a noncontact processing method, which is able to form a defect-free surface. This work aims to explore the mechanism of forming a smooth, defect-free fused silica surface by high-power density laser polishing with coupled multiple beams. The underlying mechanisms of laser polishing was revealed by numerical simulations and the theoretical results were verified by experiments. The simulated polishing depth and machined surface morphology were in close agreement with the experimental results. To obtain the optimized polishing quality, the effects of laser polishing parameters (e.g. overlap rate, pulse width and polishing times) on the polishing quality were experimentally investigated. It was found that the processing efficiency of fused silica materials by carbon dioxide (CO2) laser polishing could reach 8.68 mm2 s−1, and the surface roughness (Ra) was better than 25 nm. Besides, the cracks on pristine fused silica surfaces introduced by initial grinding process were completely removed by laser polishing to achieve a defect-free surface. The maximum laser polishing rate can reach 3.88 μm s−1, much higher than that of the traditional mechanical polishing methods. The rapid CO2 laser polishing can effectively achieve smooth, defect-free surface, which is of great significance to improve the surface quality of fused silica optics applied in high-power laser facilities.

The issues of laser-induced damage of transparent dielectric optics severely limit the development of large laser systems. In order to explore the mechanism of nanosecond laser damage on KDP surface, a multi-physics coupling dynamics model and a time resolved detection system were developed to obtain the transient dynamic behaviors of laser damage. The behaviors of laser energy transmission, thermal field distribution and damage morphology during nanosecond laser irradiation on KDP surface were simulated. It is found that the enhancement of light intensity caused by surface defect plays an important role in the initial energy deposition and damage initiation of the laser irradiation area. The evolution of the temperature field and fluid flow during subsequent laser irradiation contributes to the laser damage process. The simulated evolution of heat absorption source is verified by the transient images of local defect-induced laser damage captured by the ultra-fast experimental detection system. This work provides further insights in explaining the laserinduced damage by surface defects on KDP crystals.

Small ball-end fine diamond grinding pins dressed by on-machine electrical discharge method are promising tools for ultra-precision grinding complex structural components of hard and brittle materials. Since the electrical discharge dressing can affect the grinding pin surface morphology, it is necessary to study the wear mechanism of the metal bonded fine diamond grinding pin dressed by electrical discharge. Electrical discharge dressing experiments and fused silica grinding experiments are conducted to investigate the relationship between grinding pin wear and the dressed grinding pin surface morphology, and analyze the influence of grinding pin wear on the grinding ratio G, surface roughness, and grinding force. The metal bond recast layer, the discharge crater around the diamond grit, and the diamond graphitization are the surface morphologies of the dressed grinding pin that affect the grinding pin wear. The wear modes of the grinding pin are micro-fracture, abrasion, metal bond wear, grit pull-out. Although metal bond wear accelerates the grinding pin wear, it is prone to improve the grinding pin self-sharpening. The grinding ratio, surface roughness, and grinding force variations with the fused silica sample removal volume further verify the analysis of the dressed grinding pin wear mechanism and the self-sharpening.

Aluminum matrix composites are attractive in aerospace and automobile industry due to its low density, high strength and high corrosion resistance. Additive manufacturing methods such as selective laser melting enable the fabrication of such composites with a complex geometry, and the processing of novel, customized, tailored hybrid materials with unique hierarchical microstructures across multiple length scales. However, the microstructure evolution, wear resistance, frictional behavior under different fabrication and operation conditions of such composites still need to be explored. This study aims to fill the research gap in microstructure evolution and wear characterization of SLM-produced CNTs reinforced aluminum matrix nanocomposites. The surface characteristics, density, wear groove morphology, and surface damages in wear tests were examined. It was determined with SEM/EDS that the major phases of SLM-processed CNTs/Al-based nanocomposites were Al9Si and Si. These phases formed during the SLM process within the composites changed their wear behavior drastically. The wear surfaces were undergoing severe plastic deformation and progressive pitting. The wear rate of CNTs/AlSi10Mg nanocomposites specimens is about 33% lower than that of AlSi10Mg specimens. The higher wear resistance of the CNTs/AlSi10Mg nanocomposites specimens with shallow and narrow wear groove is attributed to the CNTs reinforcement induced higher surface hardness and also the unique hierarchical microstructure of the nanocomposites. The results showed that the SLM-produced CNTs reinforced aluminum matrix nanocomposites have good potentials to be an alternative to pure AlSi10Mg counterparts in terms of hardness, strength, frictional and wear behavior.

Herein, LiAlSiO4 was used as electrolyte material for all-solid-state electrochromic devices for the first time, and an electrochromic device (ECD) with the structure of glass/ITO/NiO/Ta2O5/LiAlSiO4/Ta2O5/WO3/ITO was prepared by magnetron sputtering method. Since LiAlSiO4 electrolyte exhibits high transparency and good ionic conductivity, the ECD shows good electrochromic performance including: large optical transmittance modulations (50.8% at 586 nm, 64.1% at 1000 nm), good stability (optical modulation is still maintained at 81.4% (586 nm) and 89.0% (1000 nm) of initial state after 1000 cycles) and high coloration efficiency (60.3 cm2 C−1 at 586 nm, 150.6 cm2 C−1 at 1000 nm). Considering the low cost and abundance of Al and Si, LiAlSiO4 may be acknowledged as a sustainable electrolyte for future high-performance ECDs.

Micro-milling can effectively remove laser damage sites on a KDP (potassium dihydrogen phosphate) surface and then improve the laser damage resistance of the components. However, the repaired KDP interfaces could cause light propagating turbulence and downstream light intensification with the potential risk to damage downstream optics. In order to analyze the downstream light field modulation caused by Gaussian mitigation pits on KDP crystals, a computational model of the downstream light diffraction based on the angular spectrum theory and the Gaussian repair contour is established. The results show that the phase offset caused by the repaired surface produces a large light field modulation near the rear KDP surface. The modulation generated in the whole downstream light field is greater than that caused by the amplitude change. Therefore, the phase characteristics of the outgoing light could be suggested as a vital research topic for future research on the downstream light field modulation caused by mitigation contours. Significantly, the experimental results on the downstream light intensity distribution have good agreement with the simulation ones, which proves the validity of the established downstream light diffraction model. The phase characterization of the outgoing light is proposed as an evaluation tool in the repair of KDP crystals. The developed analytical method and numerical discrete algorithm could be also applicable in qualifying the repair quality of other optical components applied in high-power laser systems.

In order to comprehensively reveal the surface morphology formation mechanism during CO2 pulsed laser processing of fused silica optics, the material temperature distribution, the surface morphology evolution law, as well as the relationship between laser parameters and surface quality were analyzed through three-dimensional numerical simulation and experimental research. Results showed that the residual temperature between laser pulses was lower than material’s structural transition temperature. The calculated morphologies along laser moving direction and width direction were consistent with the experimental during laser linear scanning. Besides, the superposition of spot energy during multi-pass laser scanning made the processed surface present specific three-dimensional morphology features. Laser processing lines were distributed perpendicular to the scanning direction, and the interval was equal to the track pitch. It was concluded that material’s removal depth was proportional to pulse width, and inversely proportional to the track pitch and spot moving speed. The periodic ripple structures on the surface processed by 10 μs pulsed laser were formed by the superposition of materials’ residual height during laser scanning. The conical repaired site with diameter of 2 mm and angle of 12° obtained by CO2 laser processing could completely eliminate surface damage, and laser-induced periodic surface structures were formed on the repaired surface. These studies could provide guidance for the optimization of CO2 laser processing technology and the improvement of processed surface quality.

The coating damage of SiC-coated carbon–carbon (C/C) composite is directly influenced on the anti-oxidation attack and ablation performances of carbon–carbon (C/C) composite substrate. It is unprecedentedly reported that infrared thermal-wave tomography (IR-TWT or TWT) approach with laser as external stimulation source is successfully employed for the evaluation of the SiC damage coated on the C/C composite substrate. The stimulation laser intensity is varied according to a chirp-pulsed chain, and employed to induce the chirp-pulsed radar thermal-wave signal. The thermal-wave signals of SiC-coated C/C composite dependence on coating thickness degradation and substrate material are deeply analyzed by using of one dimensional (1D) thermal-wave transfer analytical model. A temporal amplitude of thermal-wave signal as function of delay time is obtained by using of dual-orthogonal demodulation (DOD) algorithms, and it can be employed to represent thermal-wave transmission and to perform tomography. Experimental results confirm that TWT can be used to accurately and reliably assess the SiC coating damage characterization from the C/C composite substrate.

Laser excitation chirp pulsed photothermal radar imaging (CP-PRI), as a novel nondestructive testing and evaluation (NDT&E) approach, is employed to recognize the surface crack at glass fiber reinforced polymer (GFRP) composite materials. The mechanism of crack detection has been demonstrated in detail by a photothermal method and the principle of CP-PRI. A GFRP specimen with artificial surface crack is prepared for NDT&E by CP-PRI. First-order differential processing was employed to enhance edge sharpening of the amplitude image. The effects of the laser power, excitation pulsed width, reference pulsed width, delay time and chirp frequency on the signal-noise-ratio (SNR) of cracks are completely investigated. The results illustrated that the SNR of the crack is increased with the increase of laser power, the opening width of crack and excitation pulse width. The reference pulse width has few implications for the SNRs of the smaller opening width cracks (~100 μm). However, the reference initial delay time and chirp frequency had a significant influence on the SNRs of cracks. The comparison experiments between thermal wave radar imaging (TWRI) and CP-PRI has been carried out, its results indicated that the CP-PRI has the higher SNRs of cracks than that of TWRI. Consequently, CP-PRI is available for the detection of GFRP surface cracks as a result of its high detectability.

Enhancing coal permeability with formation heat treatment (FHT) is a prospective method in coalbed methane (CBM) exploitation. Here, the mechanisms of coal permeability enhancement induce by heat treatment are investigated. Residual water coal samples were heated in a helium atmosphere at 50 °C, 100 °C, 200 °C, 400 °C, 600 °C, and 800 °C in sequence. The samples’ permeability and acoustic wave velocity were measured after each heat treatment, and Young’s modulus and shear modulus were calculated to determine the change in the mechanical properties. In addition, changes in the pore structure and surface properties were analyzed with low-pressure N2 adsorption and SEM. The results indicate that in the range of 50–200 °C, the bulk water and interlayer water were removed, which alleviated the aqueous phase trapping effect, enhanced gas flow channels and increased permeability by 4–14 times. Between 400 and 600 °C, the coal samples started to pyrolysis, weakening the mechanical properties of the coal, and fractures were initiated and extended, which caused permeability to increase by 79–1400 times. After 800 °C, the surface of the coal was completely pyrolyzed, samples were cracked, and the permeability increased by more than 20,000 times. Stimulation mechanisms of FHT in CBM reservoirs consist of aqueous phase trapping alleviation, coal fractures caused by mechanical properties weakening and combustion, and finally, the C–C bond and C–O bond of molecules are broken, which induced coal fracture to produce more gas flow channels. For field application of FHT, both advantages and disadvantages are analyzed.

The intrinsic physical mechanism of CO2 laser rapid ablation mitigation micro-defects on fused silica optics surface are studied through experiments and simulations. Based on the multi-physics coupling mathematical model involving the stages of phase transition, melting flow and evaporative ablation, the calculated depth of Gaussian ablation crater and protrusion height at the edge formed by single laser pulse are 5.05 μm and 25 nm respectively, which agrees well with the experiment. Then, the temperature distribution, heat affected zone, solid-liquid transition process and surface morphology evolution under the action of moving pulsed laser are analyzed. Through studies of the relationship between laser parameters and processed surface quality, it can be concluded that the periodic structural features at the bottom of surface morphology are formed by the superposition of residual height of linear laser processing. Laser with short pulse width is more likely to cause material redeposition on the surface of fused silica optics.

The hydrophobic stability to prevent Cassie-Wenzel (C-W) transition is an important property of superhydrophobic surfaces, which is mainly controlled by the micro/nano structure of surfaces. Based on the contact lines (CLs) around and inside the contact region, we analyzed the applied forces on a static sessile droplet deposited on the hydrophobic micropillar-structured surface. A simplified double-radius fitting method was derived to outline the contour of the droplet, and a force-balance model was gained to describe the critical conditions of the C-W transition. Compared with the classical force-balance models, the theoretical predictions from the proposed model agree much better with the experimental results. A reliable estimation of the critical conditions for the C-W transition during evaporation can be readily formed by integrating the depinning mechanism of the receding CL on the micro-patterned surfaces into our model, which obviously cannot be obtained by the classical force-balance models. The effects of gravity and surface tension in the proposed equilibrium model for the C-W transition reach a compromise. The introduction of surface tension acting on the apparent CL in our model will help to provide appropriate geometric parameters for microstructures on the superhydrophobic surfaces to achieve high hydrophobic stability.