Study on Mesoscopic Stuctural Damage and Permeability Evolution of Freeze-Thaw Shale

To study the mesoscopic damage and permeability evolution of rock under freezing-thawing (F-T) cycles, freezing-thawing cycle experiments were carried out on shale under different F-T temperatures and cycles, and nuclear magnetic resonance (NMR) and permeability experiments were conducted on shale after F-T. On the basis of the experiment, the pores and permeability of the F-T shale are analyzed, and the existing permeability model is modified and improved; Therefore, the mesoscopic damage evolution characteristics and permeability evolution law of the F-T shale are obtained. It is found that with the increase in the number of cycles, the pore structure of the rock samples changes as the pore size expands and the number of pores increases, and the average porosity also increases correspondingly. It is also found that there is a good positive correlation between the increase in shale porosity and the increase in permeability. Therefore, it is believed that the increase in pore size and pore number leads to an increase in porosity, which in turn leads to an increase in permeability. On the basis of the improved SDR permeability model, the spectral area ratio parameters of large pores and fractures in the T2 spectrum were added for correction, and the number of the F-T cycles and temperature parameters were introduced to obtain the modified permeability evolution model of F-T shale. Compared with the experimental results, it is found that the modified model has good applicability. The damage law and permeability of shale under different F-T conditions are analyzed from the microscopic point of view, which has important reference significance for engineering construction in frozen soil areas.

Numerical and experimental investigation of the hole saw tool geometry effects on drilling of random chopped fiber composites

Drilling is the most widely used machining process in manufacturing holes in many industrial applications. Optimizing the drilling process is a key to improve the hole quality. Therefore, numerical modeling is an effective method that gives an idea about the cutting process to optimize the drilling parameters. This paper emphasizes the sensitivity of the thrust force, the torque and the machining-induced damage to the hole saw tool geometry using a 3D Finite Element (FE) model developed using ABAQUS/Explicit. A Johnson cook model associated with a ductile damage law is used to predict the failure mechanism of a random chopped glass fiber reinforced polyester. It is found that the thrust force, the torque and the damage around the hole obtained from the FE model are in good agreement with the experimental data. Differences of about 2% for the thrust force, 2.4% for the torque and 3% for the damage around the hole are observed. The results of the numerical model also indicated that the thrust force as well as the drilled workpiece quality are improved by choosing the suitable rake angle. A decrease of about 61% in the thrust force is observed when varying the rake angle from 0° to 20°. However, the latter has an insignificant effect on the thrust force. Furthermore, it can be concluded that this parameter highly influences the material removal process.

The mathematical expression of damage law of museum lighting on dyed artworks

Dyed artworks are highly sensitive to light and are easily affected by museum lighting, resulting in irreversible permanent color damage such as fading and discoloration. Exposure, light source spectrum and material properties are the three indicators causing damage to artworks. Therefore, it is the basis for effective lighting protection to reveal the quantitative influence of exposure and light source spectrum composition on the damage degree of different pigments and establish a mathematical model that can accurately express the above rules. At present, the color damage calculation model of dyed artworks under three parameters’ coupling action is missing. This research established a visual three-dimensional change surface of the color difference values of 23 pigments varying with the spectral wavelength and exposure through experimental methods. The relative responsivity function ΔEn = fn(λ, Q), where n = 1 ~ 23, was obtained for 23 pigments under the coupling effects of exposure and light source spectra. Furthermore, a mathematical model $$D_{n} = \mathop \smallint \limits_{380}^{780} S\left( \lambda \right) \cdot f_{n} \left( {\lambda ,Q} \right)d\lambda$$ D n = ∫ 380 780 S λ · f n λ , Q d λ calculating the color damage of pigments in the range of visible light was proposed. The proposed model was verified by the experimental method, which realizes the mathematical expression of the damage law of museum lighting on dyed artworks.

Damage Analysis of Concrete Structure under Multidirectional Shaped Charge Blasting Using Model Experiment and Ultrasonic Testing

Quantitatively analyzing multidirectional shaped charge blasting energy distribution and improving the rock-fracturing efficiency have been a challenging problem in blasting and civil engineering. In this work, we carry out four groups of concrete model experiments using ultrasonic testing, comparing conventional blasting, and multidirectional shaped charge blasting. Then, the probability and statistics method is used to quantitatively analyze the blasting damage and the energy distribution. The test results show that ultrasonic testing and statistics model can quantitatively evaluate the damage law and energy distribution of blasting. By comparing with conventional blasting method, the multidirectional shaped charge blasting with V-shaped multidirectional shaped energy groove has achieved the effect of energy accumulation. It increases the distribution of energy in the rock crack district, increases the blasting damage range, and improves the rock-fracturing efficiency of blasting. The V-shaped multidirectional shaped energy groove can be used as a new approach for rock fracturing in similar projects.

Effect of the shape of the softening damage law on the predicted tensile fracturing and energy dissipation in textile composites

The fracturing behavior of fiber-reinforced composites is often modeled using continuum damage mechanics-based approaches which commonly assume a linear softening damage law, i.e. a linearly decreasing stress with increasing strain. The objective of this paper is to assess the suitability of this assumption for composites and to systematically analyze the effect of the assumed shape of the softening damage law at material point, on the predicted fracturing behavior of the structure. The material considered is an epoxy/carbon-fiber twill woven composite. Numerical evaluations are conducted by predicting the strength size effect and progressive accumulation of damage in a structure and comparing with experimental measurements. Damage models with a wide range of shapes of softening laws are considered. These include linear, bilinear, trilinear, exponential, power law and sigmoidal. The effect of introducing a sudden drop in the damage law is also evaluated. All modeling is conducted via the crack band model (CBM), to ensure the mesh objectivity of results. It is found that despite using the right strength and fracture energy as input at the material point level, not all softening law shapes can accurately predict the strength size effect and post-peak softening. Especially the sudden drop feature leads to severe underprediction of strength. Bilinear softening shows the best combination of simplicity and accuracy, especially if formulated via the R-curve approach. Further insights are obtained by assessing the predicted fracture process zone size and fracture energy via the size effect method. Finally structure level predictions are made by considering plug initiated axial crushing of a cylindrical crushcan. The close ties between the shape of the material softening law and predicted process zone, and structural fracturing are revealed, and shown to be an important consideration in formulating damage models.