- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Laser-Induced Thermography for Quantitative Detection of Cracks in Building Materials
摘要： Laser-induced thermography is a an active technique using a laser source to heat a very small area on a side of a crack in a building material. The presence of a crack is easily detected as a sharp change in the temperature due to its insulating nature, but no information about its depth is directly available from the thermal image. The method described in this paper uses a heuristic form of the temperature on the surface of the heated specimen, which is transformed to a two-dimensional distribution. Then, a relation is used (called β-tool) between the thermal gap across the crack and the unknown depth of the damage. The purpose is that of making it possible to distinguish between shallow and deep fractures (more than 15mm deep).
关键词： laser-spot thermography,non-destructive evaluation,cracks
更新于2025-09-11 14:15:04
-
Defect induced thermal-plasma coupling damage in optical films under nanosecond pulse laser irradiation
摘要： Ten prestressed concrete beams were designed and manufactured, which were preloaded with 40% and 60% ultimate load to crack. Then the beams were reinforced by CFRP and immersed in chloride condition for 120 days. After that, a four-point bending test was performed. Based on the statistics and fractal theories, the cracking mechanism, distribution and shapes of cracks in mid span were researched, considering the initial cracks, CFRP reinforcement and chloride corrosion. The test results demonstrate that CFRP has a restraining effect on the cracks, and the effect decreases with the increases of heights. The crack widths conform to normal distribution, and the dispersion coefficient, average widths and characteristic widths decrease with the increase of the heights, and the three parameters of CFRP reinforced beams at the same heights are all smaller than those of unreinforced beams. The fractal dimensions of cracks in unreinforced beams and CFRP reinforced beams increase linearly and exponentially with load steps, respectively. CFRP reinforcement and Chloride corrosion makes the fractal dimension increase, respectively. The corrosion effect of chloride can be weakened by CFRP. Therefore, the fractal dimensions of beam cracks can be used to evaluate the damage caused by several coupled load conditions.
关键词： chloride corrosion,cracks,fractal dimension,prestressed concrete beams,CFRP
更新于2025-09-11 14:15:04
-
Analysis of multiple edge cracks in a non-homogeneous piezoelectric layer
摘要： This study is concerned with the treatment of the several edge cracks in a functionally graded piezoelectric (FGP) layer under anti-plane mechanical and in-plane electrical loading. The edge crack is assumed to be either electrically impermeable or permeable. The problem is formulated by using distributed dislocation technique. The integral equations are constructed for the analysis of a FGP layer, in which the unknown variables are dislocation densities. By use of the dislocation densities, the field intensity factors are calculated. Numerical examples are provided to show the effect of the location and orientations of edge crack upon the stress intensity factors.
关键词： functionally graded piezoelectric,distributed dislocation technique,edge cracks,stress intensity factors
更新于2025-09-10 09:29:36
-
Fatigue of Materials at Very High Numbers of Loading Cycles (Experimental Techniques, Mechanisms, Modeling and Fatigue Life Assessment) || Three-dimensional characterization of duplex stainless steel by means of synchrotron radiation X-ray diffraction imaging techniques
摘要： The combined use of X-ray diffraction contrast tomography (DCT) and X-ray phase imaging techniques like phase contrast tomography and holotomography enable non-destructive characterization of the three dimensional grain and phase microstructure in austenitic-ferritic duplex stainless steel. Phase contrast tomography highlights discontinuities of the refractive index inside a material and is therefore ideally suited for imaging fatigue cracks and phase boundaries. The acquisition of phase images at multiple propagation distances allows for the two-step procedure of phase retrieval and tomographic reconstruction of the refractive index via holotomography. Combined with appropriate regularization and segmentation techniques, this technique provides the sensitivity to discriminate the minute difference in electron density between the austenitic and ferritic constituent phases of duplex steel. X-ray diffraction contrast tomography on the other hand exploits X-ray Bragg diffraction signals of the individual crystallites and yields three-dimensional grain orientation maps for each of the constituent phases (austenite and ferrite). Merging the results of both imaging modalities, the fidelity of the inter-phase boundaries (derived from X-ray holotomography) can be used to enhance the spatial fidelity of the 3D grain orientation maps produced by DCT. We have combined this microstructure characterization scheme with time lapse observations of a propagating fatigue crack by means of repeated phase contrast tomography inspection during an interrupted fatigue test. Access to the crack growth history and the crystallographic microstructure allow for qualitative analysis of fatigue crack – microstructure interactions and provides valuable input for refinement and benchmarking of image based crystal plasticity finite element calculations.
关键词： texture,fatigue cracks,microstructural barriers,X-ray diffraction contrast tomography,residual strain,X-ray orientation imaging,annealing twins,X-ray phase contrast tomography
更新于2025-09-10 09:29:36
-
Influence of Cracks on the Optical Properties of Silver Nanocrystals Supracrystal Films
摘要： Physical properties of nanocrystals self-assembled into 3D superlattices called supracrystals are highly specific with unexpected behavior. The best example to support such claim was given, through STM/STS experiments at low temperature, of very thick supracrystals (around 1000 layers) where it was possible to image the surpracrystal surface and study their electronic properties. From previous studies, we know the optical properties of Ag nanocrystals self-assembled in hexagonal network (2D) or forming small 3D superlattices (from around 2 to 7 layers) are governed by dipolar interactions. Here, we challenge to study the optical properties of Ag supracrystals film characterized by large thicknesses (from around 27 to 180 Ag nanocrystals layers). In such experimental conditions, according to the classical Beer-Lambert law, the absorption of Ag films is expected to be very large and the film transmission is closed to zero. Very surprisingly, we observe reduced transmission intensity with an increase of the notch linewidth, in the 300-800 nm wavelength range, as the supracrystal film thickness increased. By calculating the transmission through the supracrystal films, we deduced that the films were dominated by the presence of cracks with wetting layers existing at their bottoms. This result was also confirmed by optical micrographs. The cracks widths increased with increasing the film thickness leading to more complex wetting layers. We also demonstrated the formation of small Ag clusters at the nanocrystal surface. These results provide some implications towards the design of plasmonic materials.
关键词： localized surface plasmon resonance,supracrystals,silver nanocrystal,optical properties,cracks
更新于2025-09-04 15:30:14
-
Local Strain and Crystalline Defects in GaN/AlGaN/GaN(0001) Heterostructures Induced by Compositionally Graded AlGaN Buried Layers
摘要： Plastic strain relaxation in epitaxial layers is one of the crucial factors that limit the performance of III-nitride-based heterostructures. In this work, we report on strain relaxation and crystalline defects in heterostructures consisting of compositionally graded AlGaN epitaxial layers tensile-strained between a GaN-buffer and a GaN-cap. We demonstrate the effects of Al concentration and the shape of the concentration-depth profile in the buried graded layers on the accumulated elastic strain energy and how this influences the critical thickness for crack generation or fracture. It is shown that this fracture leads to the formation of partially relaxed regions with their degree of strain relaxation directly related to the density of cracks. Nevertheless, even though the in-plane coherency between the AlGaN layer and the GaN-buffer is broken, the in-plane coherency within the AlGaN layer is preserved for all regions. Furthermore, the tensile strain released in the buried graded AlGaN layers is consistent with compressive strain induced in the GaN-cap layers. Finally, the localized stress and the densities of threading dislocations are correlated with the features of the resulting fractured heterostructures. These results are important towards the control of complex plastic strain relaxation and further facilitate the growth of high quality compositionally graded AlGaN-based devices.
关键词： X-ray diffraction,cracks,graded layers,epitaxy,strain relaxation,AlGaN
更新于2025-09-04 15:30:14