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In this paper, we continue our work on the propagation of Lamb waves in a poroelastic infinite strip containing a linear crack. In the previous work, the crack was placed horizontal to the upper and lower surfaces and moreover, there was zero pressure on the upper and lower surfaces, a physically impossible situation. In the present paper, the crack is situated perpendicular to the side and situated at the origin. A step stress is applied to the crack surface resulting in transient behavior. By using the Fourier transform and Laplace transform methods, we arrive at dual integral equations. From this formulation, we subsequently obtain, by reduction, a Fredholm integral equation of the second kind. This equation is solved numerically, and the dynamic stress intensity factor is shown graphically.

The p-silicon surfaces have been irradiated with ~ 100 MeV Si⁷⁺ions to a fluence of 2.2×10¹³ ions cm^-2, and surface morphology has been studied with atomic force microscopy (AFM). Interesting features of cracks of ~ 47 nm in depth and ~ 103 nm in width on the irradiated surfaces have been observed. The observed features seemed to have been caused by the irradiation-induced stress in the irradiated regions of the target surface.

Laser cladding is one kind of advanced surface modification technology and has the abroad prospect in making the wear-resistant coating on metal substrates. However, the application of laser cladding technology does not achieve the people's expectation in the practical production because of many defects such as cracks, pores and so on. The addiction of rare earth can effectively reduce the number of cracks in the clad coating and enhance the coating wear-resistance. In the paper, the effects of rare earth on metallurgical quality, microstructure, phase structure and wear-resistance are analyzed in turns. The preliminary discussion is also carried out on the effect mechanism of rare earth. At last, the development tendency of rare earth in the laser cladding has been briefly elaborated.

The restoration process of cracked images is a challenge and an important field of image and video processing. Old images that experienced bad treatment and environmental conditions, or images of old buildings and statues have the problem of cracks. This problem restricts the ability of extracting information and processing of the image. Many algorithms have been proposed to restore cracked images but most of them failed to remove these cracks efficiently based on realistic assumptions. So, we developed and implemented a new algorithm in order to repair cracked images efficiently by proposing new techniques such as seam processing, stochastic analysis and learning process. The basic motivation of this work is to design a simple algorithm of efficient computation complexity and memory usage that can be used in an interactive fashion where a simple set of parameters is used to control behavior and performance of the algorithm. The algorithm uses seam processing to discover cracks and local spatial information to compensate and handle information shortage based on statistical analysis and data generation. In general, the algorithm can be divided into three phases: cracks detection, cracks filling, and post-processing phase to enhance the quality. The results show how the algorithm deals with two cracked images of extreme deterioration. The results are based on subjective tests where 85 persons graded and evaluated the results under different conditions through three separate sessions.

The conventional finite element method is improved to tackle complex cracks with multiple branches. The parasitic nodes are introduced to the nodes whose nodal support is completely cut by the crack surfaces, while the nodes whose supports contain crack tips inside are accordingly enriched by the crack tip functions. The principle to set parasitic nodes is regulated, and the relation to the previous methods is dissected. The formulation of the present method is derived, and numerical experiments are conducted. The results show that the present method can treat complex cracks conveniently and efficiently, and the unknowns have a clear physical interpretation.

A simplified meshless methods for brittle fracture and nonlinear material is presented. In this method, the crack is modeled by a set of discrete crack segments crossing the entire domain of influence of the meshless shape functions. The key advantage of this method is its simplicity since no representation of the crack topology is needed. A nonlocal stress tensor around the crack tip is used as fracture criterion. A neo-Hooke material in the bulk material is used and a cohesive zone model is employed once discrete cracks occur. We also present consistent linearization of the cohesive zone model. The method is applied to fracture modeling in concrete that is accompanied by excessive cracking and therefore methods that represent the crack path have major drawbacks. We demonstrate the accuracy of the proposed method for complex problems involving mode-I and mixed mode failure.

The slender circle submarine pipeline possesses both shell and beam characteristics, which are widely used in practical engineering. Unfortunately, for some reason, there will be some geometric defects in the cross-section of the pipeline (such as machining errors and seawater corrosion, etc.), resulting in the stiffness of the circular submarine pipeline being different. The cracked variable stiffness pipeline is actually a typical three-dimensional complex crack problem. In this paper, taking the outer circle and inner ellipse submarine pipeline as an example, a method based on elementary mechanics and the concept of the conservation law is proposed to determine the stress intensity factors (SIFs) of variable stiffness pipeline, and a series of closed-form expressions of SIF are derived for the cracked pipeline. The results from the present method are shown to agree well with available solutions and FEM. In particular, the present method can also be easily applied to other similar variable stiffness submarine pipelines.

Serious microcracks often occur on the surface of nanohydroxyapatite (n-HAP) artificial bone scaffolds prepared by selective laser sintering (SLS) technology. In this study, we found that appropriate preheating before sintering can reduce and attenuate the cracks. The microstructure and morphology of sintered n-HAP were tested at different preheating temperature and laser sintering speed with scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The experiments showed that the cracks gradually reduced and then disappeared when the preheating temperature increased from 0°C to 600°C while other parameters remain unchanged. The n-HAP particles gradually fused and grew up, while the grain size of sintered n-HAP will be attenuated with the increase of preheating temperature. As the thermal conductivity of n-HAP increases with increased preheating temperature, the temperature drops quickly, inhibiting greatly the grain growth of n-HAP. We obtained a group of optimum parameters when the sintered n-HAP still maintains nanostructure and possesses the optimal comprehensive performances, that is, laser power is 26 W, spot diameter is 4 mm, sintering speed is 200 mm/min, layer thickness is 0.4 mm, layer density is 852 kg/m³, and optimized preheating temperature is 600°C. These data illustrated that the cracks of sintered n-HAP can be eliminated at appropriate preheating temperature and sintering speed. This provided experimental optimal condition for the preparation of artificial bone scaffolds with nanohydroxyapatite ceramics.