Damage Evolution of Concrete Piles Mixed with Admixtures in Marine Corrosion and Freeze-Thaw Environment

Marine corrosion and freeze-thaw environment will bring serious damage to marine concrete structures, leading to affect the safety and service life of structures. With the help of artificial climate and environment simulation laboratory, the variation of the compression strength and elastic modulus of concrete with the number of freeze-thaw cycles and corrosion time under the corrosion and freeze-thaw environment is studied. The results show that both of them firstly increase and then decrease with corrosion time. When the corrosion time is 270 d and the freeze-thaw time is 90 times, the strength of concrete decreases by 13% and the elastic modulus decreases by 5%. Then, based on the theory of damage mechanics, the damage evolution and constitutive model of concrete under the marine corrosion and freeze-thaw environment are established. Compared with the experimental results, it is found that the model can well describe the damage evolution characteristics of concrete under marine corrosion and freeze-thaw environment. Finally, a numerical model is established on the basis of elastic modulus and strength degradation model of concrete under marine corrosion and freeze-thaw environment. Elevated pile caps of concrete pile component are taken as an example to analyze the process of damage, and the change rules of displacement, deformation, and damage of concrete pile are obtained.

Study on the Damage Evolution Process and Fractal of Quartz-Filled Shale under Thermal-Mechanical Coupling

Filling of brittle minerals such as quartz is one of the main factors affecting the initiation and propagation of reservoir fractures in shale fracturing, in order to explore the failure mode and thermal damage characteristics of quartz-filled shale under thermal-mechanical coupling. Combining the theory of damage mechanics and thermoelasticity, RFPA2D-Thermal is used to establish a numerical model that can reflect the damage evolution of shale under thermal-solid coupling, and the compression test under thermal-mechanical coupling is performed. The test results show that during the temperature loading process, there is a temperature critical value between 60°C and 75°C. When the temperature is less than the critical temperature, the test piece unit does not appear obvious damage. When the temperature is greater than the critical temperature, the specimen unit will experience obvious thermal damage, and the higher the temperature, the more serious the cracking. Under the thermal-mechanical coupling of shale, the tensile strength and elastic modulus of shale show a decreasing trend with the increase of temperature. The failure modes of shale under thermal-solid coupling can be roughly divided into three categories: “V”-shaped failure (30°C, 45°C, and 75°C), “M”-shaped failure (60°C), and inverted “λ”-shaped failure (90°C). The larger the fractal dimension, the more complex the failure mode of the specimen. The maximum fractal dimension is 1.262 when the temperature is 60°C, and the corresponding failure mode is the most complex “M” shape. The fractal dimension is between 1.071 and 1.189, and the corresponding failure mode is “V” shape. The fractal dimension is 1.231, and the corresponding failure mode is inverted “λ” shape.

Collapse Mechanism of Single-Layer Cylindrical Latticed Shell under Severe Earthquake

In this paper, the results of finite element analyses of a single-layer cylindrical latticed shell under severe earthquake are presented. A 3D Finite Element model using fiber beam elements is used to investigate the collapse mechanism of this type of shell. The failure criteria of structural members are simulated based on the theory of damage accumulation. Severe earthquakes with peak ground acceleration (PGA) values of 0.5 g are applied to the shell. The stress and deformation of the shell are studied in detail. A three-stage collapse mechanism “double-diagonal -members-failure-belt” of this type of structure is discovered. Based on the analysis results, measures to mitigate the collapse of this type of structure are recommended.

Collapse Mechanism of Single-Layer Cylindrical Latticed Shell Under Severe Earthquake

In this paper, the results of finite element analyses of a single-layer cylindrical latticed shell under severe earthquake is presented. A 3D Finite Element model using fiber beam elements were used to investigate the collapse mechanism of this type of shell. The failure criteria of structural members are simulated based on the theory of damage accumulation. Severe earthquake of peak ground acceleration (PGA) of 500 gal was applied to the shell. The stress and defeomation of the shell were studied in detail. A three-stages collapse mechanism “double-diagonal -members-failure-belt” of this type of structure was discovered. Based on the analysis results, the measures to mitigate collapse of this type of structure is recomanded.

Modern theory of fracture of deformable materials

Researches and developments on creation of the theory of damage and destruction of deformable isotropic and anisotropic materials are stated. The proposed model and criteria to predict the destruction of the monotonic, non-monotonic, including the alternating cyclic loading. From the proposed criteria in the limiting special cases follow the known criteria used in predicting failure under monotonic loading, as well as cyclic loading, leading to fatigue failure. Possibility of application of the offered models and criteria for design and optimization of processes of processing of materials is shown.

Research on the Damage Identification of Weld Metal Cracking of Metal Structure Based on PVDF

A new detection method for measuring weld crack of crane’s metal structure is developed.It works by combining polyvinylidene fluoride (PVDF) with curvature operational shapes (COS) algorithm. First, the theory of damage identification using the imaginary part of frequency response function was analyzed, and the extraction approach of COS was illuminated in detail. Then, the fitting method which is called gapped-smoothing method (GSM) was chosen to obtain the COS of healthy structure.Next, experiments were carried out on a steel plate with weld cracks based on PVDF. The experiment result expresses that the positions of cracks could be located precisely and the index is very sensitive to the different length of cracks. Therefore it can provide reliable information for positioning and quantitative analysis of the weld cracks.

The Loosen Circle Radius Based on the Theory of Damage Mechanics

<p class="ordinary-outputtarget-output">After surrounding rock is disturbed by some damage form a loosen circle in surrounding rocks of a roadway, in order to solving the range of loosen circle, mechanical mechanism of loosen circle was discussed on the basis of damage mechanics and loosen circle radius calculation formula proposed. This work has some certain reference for roadway support design.</p>