Crack Evolution Characteristics and Cracking Mechanism of Red Beds in Central Sichuan during Seepage and Swelling

Crack is one of the important factors affecting the engineering characteristics of expansive rock and soil. In order to study the evolution characteristics and cracking mechanism of red beds in Central Sichuan during seepage and swelling, multiple groups of cracking tests are conducted under different initial states with a self-made device. In addition, combining swelling-softening mechanism of expansive rock and numerical analysis, the swelling-cracking mechanism is studied. The following research results are obtained. (1) The evolution process of swelling cracks is divided into three stages: the generation stage, the rapid development stage, and the stabilization stage. In the rapid development stage, the increase in the crack degree accounts for 90% of the whole process. (2) The final crack degree of the sample is related to the initial water content, water absorption method, and clay mineral content. The lower the initial water content, the greater the final crack degree of the sample. The final crack degree under the soaking water absorption method is greater than that under the capillary water absorption method, and the final crack degree of mudstone is greater than that of argillaceous sandstone and sandstone. (3) The development of swelling cracks is controlled by three significant values of water absorption, which are w 1 , w 2 , and w 3 , respectively, representing the beginning of cracking, the starting of the rapid development stage, and the starting of the stabilization stage. Among them, w 2 is of great significance in engineering practice. It shows that the development of cracks has entered a stage of rapid development, and the crack degree in this stage will increase exponentially with water absorption. (4) Uneven water absorption and uneven distribution of clay minerals lead to uneven swelling of expansive rock, which in turn generates swelling stress. Under the combined action of swelling stress and water swelling-softening, the internal structure of the rock is destroyed, leading to the generation and development of the cracks. Due to the different causes of uneven expansion, the mechanical mechanism of cracking and the shape of the resulting cracks will be different.

Experimental and Numerical Study of Lattice Girder Composite Slabs with Monolithic Joint

This paper studies the behavior of lattice girder composite slabs with monolithic joint under bending. A full-scale experiment is performed to investigate the overall bending resistance, deflection and the final crack distribution of latticed girder composite slab under uniformly distributed load. A finite element model is given for the analysis of the latticed girder composite slabs. The effectiveness and correctness of the numerical simulations are verified against experimental results. The experimental and numerical studies conclude that the lattice girder composite slabs conform to the requirement of existing design codes. A parametric study is provided to investigate the effects of lattice girder with following conclusions: (a) the lattice girder significantly increases the stiffness of the slab when comparing with the precast slab without reinforcement crossing the interface; (b) the additional reinforcement near the joint slightly increases the stiffness and resistance, while it prevents damage near the joint.

Simulation Study of the Damage Mechanisms Appearing in a Cross Ply Composite Material Loaded in Uniaxial Tension

The objective of this paper is to predict the different damage mechanisms in multiple scales that can occur in a cross ply composite material loaded in uniaxial tension. The simulated composite material consists of four epoxy-glass fibre layers [0/90]s and the material of each layer is transversely isotropic with viscous effects that occurred from micromechanical homogenization using Mori-Tanaka formulation, extended for visco-elastic materials. For the prediction of the cracking and interlaminar delamination, cohesive contacts were used and the final crack density results were compared with the corresponding experimental ones. Finally a microscale analysis was performed in a Representative Volume Element (RVE) to observe the matrix cracking behaviour in smaller scale.

Evolution of Cracks in Nano-CaCO3 Modified Pre-Disintegrated Carbonaceous Mudstone Under Cyclic Wetting and Drying

To explore the evolution of cracks in the pre-disintegrated carbonaceous mudstone, wetting-drying tests were carried out on nano-CaCO3 modified pre-disintegrated carbonaceous mudstone samples. The samples were prepared with aqueous solutions of different pH values. Scanning electron microscopy (SEM) was performed to clarify the mechanism of crack evolution of pre-disintegrated carbonaceous mudstone modified by nano-CaCO3. The results showed that development of shrinkage and cracks was basically divided into three stages, i.e., the gestation stage, the rapid development stage and the stable stage. For the samples without nano-CaCO3, the final crack rates and pore sizes of samples with pH = 3 and pH = 11 were larger than corresponding values of the sample with pH= 7. Moreover, final crack rate and pore size significantly decreased with the addition of nano-CaCO3 suggesting that nano-CaCO3 can effectively improve cracking resistance of pre-disintegrated carbonaceous mudstone.

Effect of geotextile on reduction of reflective cracking induced by traffic load in asphalt concrete

Cracks appear in the early cement stabilisation base due to shrinkage. Pavement service life is reduced by the reflecting cracks under load coupled with environment. Geosynthetics can be used as an effective anti-reflective crack material to improve the asphalt concrete performance. Related studies mainly focus on the optimal material type and placement location of geosynthetics. However, the mechanism research of anti-crack propagation is limited and needs further investigation. The methods used to date are hard to reveal the anti-reflective crack mechanism of geosythetics. Therefore, geosynthetic materials cannot be used appropriately. Propagation and resistance characteristics of traffic induced reflective cracks with geotextile placed in the asphalt layer was investigated using extended finite element model. The effects of geotextile placement and tensile modulus were also investigated. Compared with other zones, the geotextile stress over the crack was significantly larger. The geotextile absorbed 15% of the total stress in the asphalt surface layer. The crack propagation stages and final crack length was separate when tensile modulus of geotextile reached 50 MPa. The geotextile with 100 MPa tensile modulus was found to produce the optimal effect on preventing crack. Geotextile placed at a quarter depth of the asphalt layer from the bottom had the best crack resistance.

The solute mechanical properties impact on the drying of dairy and model colloidal systems

The impact of solute properties on the morphological characteristics of evaporating droplets is investigated through the analysis of drying stages and final crack pattern of biological samples (WPI, whey protein) and model silica dispersions (TM50).

Probabilistic Assessment of Crack Failure of Reactor Pressure Vessel (RPV) Cladding Material

To design a Reactor Pressure Vessel (RPV), material property like crack must be considered as it is an unavoidable property of materials. Presence of crack in materials must be kept within limit to prevent material’s failure. So, crack propagation must be analyzed and observed. In this paper, crack propagation due to stress and materials fracture toughness of reactor pressure vessel cladding has been observed to estimate cumulative probability of crack failure using Probabilistic Fracture Mechanics (PFM). Average crack size is guessed as 3 mm and geometry factor is considered as 1.12 to analyze edge crack. Final crack analysis range has been found to be 1.8 mm with crack propagation rate of ± 30% of its average size. Variation of critical crack size and crack initiation point for several design stresses and fracture toughness has been investigated with probabilistic fracture mechanics technique. The observed crack propagation by calculating final crack size and the cumulative crack failure probability of the reactor pressure vessel materials are presented in this work.Journal of Bangladesh Academy of Sciences, Vol. 41, No. 2, 237-245, 2017

Cracking Tendency of Self-Compacting Concrete Containing Crumb Rubber as Fine Aggregate

The utilization of crumb rubber particles extracted from waste tires in the production of self-compacting concrete (SCC) is a decent and sustainable solution to mitigate the impacts of such waste on environment. The aim of this study is to evaluate the cracking tendency of SCC with different content of crumb rubber extracted from waste tires. Five SCC mixtures were prepared. The reference mix was made with natural sand while the other four mixes were made with crumb rubber in which the natural sand was volumetrically replaced by crumb rubber at ratios of 10 %, 20 %, 30 % and 40 %, respectively. The results show that the addition of crumb rubber delays the cracking of concrete. The cracking time increases with the increase of the rubber content. The results also reveal that the addition of rubber particles not only increases the cracking time but also reduces the initial and final crack width.

Crack Growth Rates of Vertical Split Rim Wheel Failures

The fatigue crack growth rates of three vertical split rim (VSR) wheel fractures are calculated using the Paris-Erdogan fatigue crack growth equation. Initial crack length, final crack length were measured for three wheels that have experienced VSR failures. The results of the calculations indicate the lives after crack initiation are relatively short. The results of these calculations indicate the timely reduction of the number of VSR failures should emphasize the prevention of the initiation of the VSR cracks.

A Mixed Damage Model for Simulating Delamination of Composite T-Joint Components

A mixed cohesive damage model was introduced in this paper to study the delamination of composite T-joint components under pulling load. Prediction together with part of test results was presented in this paper. Modelling prediction had a good agreement with experimental work. This study indicated that the mixed damage scale plays an important role in the progressive damage analysis of T-joint components. The mixed damage scale properly reflected the effects of interaction between different damage modes in simulating damage propagation of an object with strong coupled effects. This coupled damage effect was considered from the material softening stage to final crack. Thus a proper damage accumulation was accounted since materials begin damage. An example given in this paper shown the delamination in the deltoid region of T-joint was simulated very well. Finally, a concept of novel materials was proposed for the deltoid region of T-joint in this paper. Initial investigation by simulating delamination presented that the damage resilience of composite T-joint with novel composite materials in deltoid region significantly improved its damage resilience.