Fatigue failure is the most common failure mode of structural materials. In this study, the high-cycle fatigue properties at different temperatures, fracture surface morphologies and corresponding damage mechanisms of a widely used vermicular graphite cast iron RuT450 were investigated. It is found that the fatigue strength of RuT450 decreases with the increase of temperature, and the decreasing rate is affected by the change of morphology and content of graphite. In general, the cracks initiated from the graphite phase boundary and propagated through the pearlite lamellae. In addition, according to the change of matrix micro-structure and the slight change of graphite morphology at different temperatures, and combined with the change of crack propagation threshold value under different temperature conditions, a fatigue strength prediction method for vermicular graphite cast iron at different temperatures was proposed in this work, which has high prediction accuracy.
The Nanpu Sag is a hydrocarbon-rich sag in the Bohai Bay Basin of China that underwent multiple structural deformation in the Cenozoic era, resulting in complex fault systems. Clear transtensional fault systems are present in a trapezoidal structural belt, and this setting is an ideal location to study the genesis and evolution of transtensional faults. Based on the interpretation of 3D seismic data, assembly of faults from coherent slices of seismic reflection surfaces, and analogue experiments, the geometry and kinematics of the structural belt in the Nanpu Sag were analyzed. Additionally, from the identification of structures, paleo-stress reconstruction, a model of the evolution of the trapezoidal structural belt was determined. This process requires the statistics of fault throw–displacement, variation of the formation thickness, and a specific analogue model. The results are as follows: (1) The Nanpu Sag has experienced different evolution stages, including a NW–SE extension stage in the Shahejie Formation, a N–S extending stage in the Dongying Formation, a thermal subsidence stage in the Guantao Formation, and a structural reactivation stage in the Minghuazhen Formation. (2) The direction of stress field intersected with a pre-existing strike-slip fault at a large angle for a long period, which firstly caused the fault to be separated, and then in the northern segment, the strike-slip faults reconnected with the newly generated normal faults, forming large-scale arc faults. These processes created displacement transfer through a relay ramp. (3) Analogue experiments show that the Cenozoic structural belt formed under the influence of pre-existing faults, stress field transformation, and a basal decollement layer. The simulation results are also useful for elucidating boundary conditions and fault properties, i.e., respective dynamic background and material properties.
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