Oblique Y-groove cracking test of the welding cold cracking susceptibility of domestic X-70 pipeline steel

Gas Transmitting From West to East Project' is significant. It should ensure the welding quality and safety of pipeline. The task is very arduous to guarantee the quality of the project in the condition of long line, complex weather and geology features. In this paper, the welding cold cracking susceptibility of domestic X 70 pipeline steel adopted by the project, which is one of the most interesting questions of welding quality about petrol pipeline, was studied by means of oblique Y groove cracking test. The crack ratio of surface and section was tested under the conditions of different welding materials and preheat temperature .The thickness of plate steel was 14.7 mm and 10.3 mm . The results reveal that X 70 pipeline steel has good crack resistance. The research has important value for the construction of large scale pipeline engineering and the application of domestic X 70 pipeline steel.

Numerical simulation of plate rigid restraint cracking tests based on cohesive element model

Cohesive element is developed from the Dugdal-Barenblatt model in the field of fracture mechanics. The mechanical constitutive relation of cohesive element can be artificially assumed depending on the specific applications. It has been successfully applied in the study of crystal plasticity/brittle fracture process and decohesion between delaminations. In this paper, tensile experiments of large steel plate with different length of pre-existing cracks are conducted. Based on commercial software ABAQUS, cohesive element is adopted to simulate the tensile tests, and appropriate parameter values are obtained by fitting displacement-force curves. Using these parameters, a numerical method is presented by applying cohesive element to thermo-elastic-plastic finite element method （TEP-FEM） to simulate plate rigid restraint cracking （PRRC） tests. By changing constitutive relation of cohesive element, dimensions of the model and welding conditions, the influence of welding restraint intensity and welding conditions on the crack propagation are discussed, respectively. Three types of welding cold cracking are simulated. Significant influence of welding cold cracking on resistant stress in welding line is captured by this numerical method.

Evaluation of Cracking Resistance of Copper-Bearing Age Hardening Steel Weldment

The weldability of a low-carbon copper-bearing age hardening steel was evaluated using cracking suscepti- bility calculation, HAZ maximum hardness measurement, and Y-groove cracking evaluation test. The results show that the hardenability characteristics and cold cracking susceptibility of the steel are very low. The results also indicate that a crack-free weldment can be obtained during the welding of this type of steel even at an ambient temperature as low as -5 ℃ as well as in an absolute humidity lower than 4 000 Pa without any preheat treatment. A slight preheat treatment can prevent the joint from cracking when welding is carried out at lower ambient temperature or higher absolute humidity.

Fractal characteristics of cracks and fragments generated in unloading rockburst tests

True triaxial rockburst experiments with four different unloading rates were performed on four prism specimens of granite sampled from Beishan, China. The damage evolution in the rockburst test was investigated from two aspects including fracture surface crack and fragment characteristics. The scanning electron microscopy was used to observe the micro crack information on fragment surface. Combing binarization and box counting dimensions, the fractal dimensions of cracks were obtained. Meanwhile,the fragments were collected and a sieving experiment was conducted. We weighed the fragments qualities, counted the amount of fragments and measured the fragments length, width and thickness.Utilizing four methods to calculate damage fractal dimensions of fragments, the trend of fractal value changing with unloading rates can be roughly described. It can be concluded from these experiments that the fractal dimension either for crack or for fragment holds a decreasing trend with the decreasing unloading rate, indicating a reduction of damage level.

Application of orthogonal design in the experiment of plasma arc powder surfacing technology

In this paper, the influence of plasma arc powder surfacing technical parameters on the property of layer is defined using the orthogonal design. By the orthogonal polynomial regression, when plasma arc powder surfacing is used on the surface of the X65 steel plate with the Fe-07 alloy powder, the optimum technical parameters are the following: I=180～190 A , G=41.5 g/min , v=102 mm/min , T_0=350 ℃ , Q_l=280 L/h , Q_s=400 L/h . Further, analysis of the cracking test data showed that the cracking preheat temperature is 350 ℃ .

Monte-Carlo Simulation of Surface Crack Growth Rate for Offshore Structural Steel E36-Z35

The Monte- Carlo method is used to simulate the surface fatigue crack growth rate for offshore structural steel E36-Z35, and to determine the distributions and relevance of the parameters in the Paris equation. By this method, the time and cost of fatigue crack propagation testing can be reduced. The application of the method is demonstrated by use of four sets of fatigue crack propagation data for offshore structural steel E36-Z35. A comparison of the test data with the theoretical prediction for surface crack growth rate shows the application of the simulation method to the fatigue crack propagation tests is successful.

Shear-resistant behavior of light composite shear wall

Shear test results for a composite wall panel in a light composite structure system are compared with test results for shear walls in Japan.The analysis results show that this kind of composite wall panel works very well,and can be regarded as a solid panel.The composite wall panel with a hidden frame is essential for bringing its effect on shear resistance into full play.Comprehensive analysis of the shear-resistant behavior of the composite wall panel suggests that the shear of the composite shear wall panel can be controlled by the cracking strength of the web shearing diagonal crack.

Evaluation of mixed mode-Ⅰ/Ⅱ criteria for fatigue crack propagation using experiments and modeling

In this study, in-plane mixed mode-Ⅰ/Ⅱ fatigue crack growth simulations and experiments are performed for the Al 7075-T651 aluminum alloy which is widely used in the aerospace industry. Tests are carried out under different mode mixity ratios to evaluate the applicability of a fracture criterion developed in a previous study to mixed mode-Ⅰ/Ⅱ fatigue crack growth tests.Results obtained from the analyses and experiments are compared with existing and developed criteria in terms of crack growth lives. Compact Tension Shear（CTS） specimens, which enable mixed mode loading with loading devices under different loading angles, are used in the simulations and experiments. In an effort to model and simulate the actual conditions in the experiments, crack surfaces of fractured specimens are scanned, crack paths are modeled exactly, and contacts are defined between the contact surfaces of a specimen and the loading device for each crack propagation step in the analyses. Having computed the mixed mode stress intensity factors from the numerical analyses, propagation life cycles are predicted by existing and the developed mixed mode-Ⅰ/Ⅱ criteria and then compared with experimental results.