Hydrostatic stress

About: Hydrostatic stress is a research topic. Over the lifetime, 1568 publications have been published within this topic receiving 37773 citations.

Prediction of Hydrogen Induced Delayed Fracture Initiation Time of High Strength Steel Using Cohesive Zone Modeling

Abstract: A sequential coupling calculation method on hydrogen induced delayed fracture was developed based on cohesive zone modeling(CZM) by using finite element program-ABAQUS.Using this method,the fracture initiation time was numerically predicted for circumferentially notched round bar specimen of AISI4135 high strength steel under a constant load after electrochemically pre-charged.The effect of various hydrogen contents was also considered.The results show that the hydrogen dependent CZM can be used in the prediction of failure in actual structures.The predictions of the time to fracture are in good quantitative agreement with the some experimental results.The delayed fracture occurrs when a critical hydrogen concentration at the location of max hydrostatic stress is reached by diffusion.The critical hydrogen concentration is not dependent on initial hydrogen content.

Analysis of Hydrogen-Assisted Brittle Fracture Using Phase-Field Damage Modelling Considering Hydrogen Enhanced Decohesion Mechanism

Abstract: This study proposes a hydrogen-assisted fracture analysis methodology considering associated deformation and hydrogen transport inside a phase-field-based formulation. First, the hydrogen transport around a crack tip is calculated, and then the effect of hydrogen enhanced decohesion (HEDE) is modeled by defining the critical energy release rate as a function of hydrogen concentration. The proposed method is based on a coupled hydrogen mechanical damage under phase-field and implemented through a user subroutine in ABAQUS software. The test using compact tension (CT) sample is investigated numerically to study the hydrogen embrittlement on 45CrNiMoVA steel. Experimentally, the microstructural fracture presents a mixed brittle fracture mode, consisting of quasi-cleavage (QC) and intergranular (IG) fracture with hydrogen. This fracture mode is consistent with the suggested HEDE mechanism in the model. The simulation results show that hydrogen accumulates at the crack tip where positive hydrostatic stress is located. Moreover, the model estimates the initial hydrogen concentration through iterations. The simulated load-line displacement curves show good agreement with the experimental plots, demonstrating the predictive capabilities of the presented scheme.

Primitive stress in the underground mines at Kitwe-Nkana area Zambia, Africa

Abstract: At the Kitwe-Nkana copper-bearing structure there are two underground mines: Mindola Mine and Nkana Mine. The original design for underground mining was on the traditional assumption that the principal load was to the weight of roofing sediments, and that horizontal stresses are equal to one-third of the vertical stresses. But during mining excavation into deeper levels, it was realized that the lateral stress is greater than the vertical (active tectonic lateral stress field), also that stressed and unstressed zones (passive tectonic stress), depend on structure geometry, that in the deeper part an almost hydrostatic stress (frozen stress field) exists and finally a zone with high stress concentration (pressure zone). It appears that after a certain depth vertical stresses and lateral stresses vary considerably in orientation and magnitude. The direction of the major principal stress is perpendicular to the bedding plane, and minor principal stress along the bedding plane. In this paper the quality of the compound of virgin stress in the ore formation is assumed on the basis of the relationship between geometry and physics of geological structures and primitive stress, as well as on the basis of underground stress measurement data.

Neutron Diffraction Measurements of a Thermally Fatigued Single Crystal Superalloy

Abstract: The thermally fatigued single crystal superalloy DZ125L is investigated by neutron diffraction measurements. The measurements, made using the phi angle oscillating method, provide more detailed and reliable data than those with the phi angle fixed. Diffraction studies show that the influence of thermal fatigue on the lattice parameters of the alloy is very limited. The stress analysis reveals that triaxial elastic hydrostatic stress plays a major role during thermal fatigue. The magnitude of the macrostress increases with the fatigue cycles, with the stress of the gamma phase increasing more significantly than that of the gamma' phase, and becoming fragile after many cycles. The changes in the microstrain are dependent on the reflection planes. The microstrains at the center of the sample are released by the thermal fatigue in comparison with those at the outlying locations, which has been attributed to the advance of the dislocation slips.