Resistance of isotropic graphite materials to deformation and fracture under complex stress conditions

1979 ◽  
Vol 11 (2) ◽  
pp. 182-188
Author(s):  
A. V. Berezin ◽  
E. V. Lamakin ◽  
V. I. Strokov ◽  
V. N. Barabanov
Keyword(s):  
Complex Stress ◽  
Stress Conditions ◽  
Deformation And Fracture ◽  
Isotropic Graphite

Patterns of deformation and fracture in molybdenum alloy under complex stress conditions

1976 ◽  
Vol 8 (7) ◽  
pp. 777-780
Author(s):  
F. F. Giginyak ◽  
V. V. Bashta ◽  
A. A. Lebedev ◽  
V. K. Kharchenko
Keyword(s):  
Complex Stress ◽  
Stress Conditions ◽  
Molybdenum Alloy ◽  
Deformation And Fracture

Failure behavior of multi-state system considering functional and physical isolation effects

2021 ◽  
pp. 1748006X2110418
Author(s):  
Ying Chen ◽  
Ze Wang ◽  
Yanfang Wang ◽  
Rui Kang
Keyword(s):  
Transition Probabilities ◽  
Functional Dependence ◽  
Great Difficulty ◽  
Complex Stress ◽  
State System ◽  
Stress Conditions ◽  
State Transitions ◽  
Failure Behavior ◽  
Physical Isolation ◽  
Isolation Effects

The multi-state system (MSS) is a system that may exhibit multiple states or performance levels. Most existing studies assumed that the transition probabilities from states to states are known. However, in practical engineering, the complex stress conditions lead to great difficulty of collecting the statistical data of state transitions. In this paper, based on physics-of-failure theory, we consider different levels of damages caused by failure mechanisms (FMs) are the main reasons to components’ multiple states. Besides, the physical isolation (PI) effect on degradations of FMs is also studied, which is neglected in the existing studies about the MSS with functional dependence groups. Decision-diagram based methods are used for modeling the failure behavior of the MSS. An automatic collision avoidance system is analyzed for illustrating the proposed modeling and analyzing methods. The results show that comparing to the results without the consideration of PI effect, the probabilities of different states with PI effect of multi-state components and system may decrease or increase, which depends on the actual PI effects to the stress conditions.

High-Temperature Creep Tests of Two Creep-Resistant Materials at Constant Stress and Constant Load

2019 ◽  
Vol 827 ◽  
pp. 246-251
Author(s):  
Vàclav Sklenička ◽  
Květa Kuchařová ◽  
Marie Kvapilová ◽  
Luboš Kloc ◽  
Jiří Dvořák ◽  
...  
Keyword(s):  
Creep Behaviour ◽  
Constant Load ◽  
Complex Stress ◽  
Constant Stress ◽  
Fracture Mechanisms ◽  
Stress Tests ◽  
Creep Tests ◽  
Deformation And Fracture ◽  
Dependent Component ◽  
The Difference

Creep is defined as a time dependent component of plastic deformation. Creep tests can be performed either at constant load or at constant applied stress. Engineering creep tests carried out at constant load are aimed at determination of the creep strength or creep fracture strength, i.e. the data needed for design. The constant stress tests are important as a data source for fundamental investigations of creep deformation and fracture mechanisms and for finite element modelling of more complex stress situations. For some materials, the difference between the two type of testing can be very small, while for other materials is large, depending on the creep plasticity of the material under testing. The paper aims to compare the creep results of two different creep-resistant materials: the advanced 9%Cr martensitic steel (ASME Grade P91) and a Zr1%Nb alloy obtained by both testing methods and to clarify the decisive factors causing observed differences in their creep behaviour.

scholarly journals INVESTIGATION OF MULTI-CYCLE FATIGUE OF EQUIPMENT AND MACHINERY ELEMENTS UNDER COMPLEX STRESS CONDITIONS AND NON- STATIONARY LOADING

2020 ◽  
Vol 3 (77) ◽  
pp. 11-17
Author(s):  
S. J. JASEN ◽  
◽  
D. K. JAKIYEV ◽  
S. S. ZHUNISBEKOV ◽  
◽  
...  
Keyword(s):  
Experimental Data ◽  
Fatigue Life ◽  
Cyclic Stress ◽  
Complex Stress ◽  
Stress Conditions ◽  
Energy Concentration ◽  
Structural Elements ◽  
Cycle Fatigue ◽  
Stationary Loading ◽  
Comparison Of The Results

A computational and experimental method for estimating the fatigue life of structural elements of machines operating under complex cyclic stress conditions and non-stationary loading is considered. Comparison of the results of the calculations and experimental data indicated the effectiveness of the kinetic equation of multi-cycle fatigue damage based on the energy concentration of fatigue failure.

Improving fracture initiation and potential impact on fracture coverage by implementing optimal well-planning and drilling methods for typical stress conditions in the Cooper Basin, central Australia

2015 ◽  
Vol 55 (2) ◽  
pp. 403 ◽  
Author(s):  
Raymond Johnson ◽  
Hani Abul Khair ◽  
Rob Jeffrey ◽  
Jeremy Meyer ◽  
Carly Stark ◽  
...  
Keyword(s):  
Numerical Models ◽  
Model Development ◽  
High Stress ◽  
Fracture Initiation ◽  
Horizontal Stress ◽  
Complex Stress ◽  
Stress Conditions ◽  
Natural Fractures ◽  
Fracture Conductivity ◽  
Cooper Basin

Drilling conditions involving high mean and deviatory stresses, and natural fractures in the Cooper Basin present challenges in drilling and introduce wellbore rugosities, leaving a damaged wellbore subject to a stress cage effect. Fracture initiations have been problematic in vertical Cooper Basin wells, exhibiting high initiation and treating pressure frac treatments, and with high stress conditions posing greater risks in non-vertical completions. While far-field fracture complexity should be simplified, the near wellbore complexity results in reduced fracture conductivity. The authors believe that present drilling practices and wellbore azimuths may be contributing to sub-optimal hydraulic fracture initiations and complexities. Present analytical modelling methodologies can derive initiation pressures for circular wellbores, but require more complex numerical models to include flaws and ellipticity to represent natural fractures and wellbore rugosities. This study compares initiation pressures and presents graphical results, comparing circular and elliptical wellbore cases with flaws. This extended abstract outlines the criteria used in these models and remarks on areas needing further research and model development. The authors also propose improved drilling techniques to achieve more stable, smoother wellbores, potentially reducing some rugosity and drilling induced fractures. By using data from recent research and other cases with complex stress environments, it is proposed that initiation pressures might be reduced by inclining wells for hydraulic fracturing treatments in a favourable alignment in the maximum horizontal stress direction (σH-Max), and implementing completion techniques that aid better fracture initiation.

scholarly journals Investigation of the Energy Evolution of Tectonic Coal under Triaxial Cyclic Loading with Different Loading Rates and the Underlying Mechanism

Energies ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 8124
Author(s):  
Deyi Gao ◽  
Shuxun Sang ◽  
Shiqi Liu ◽  
Jishi Geng ◽  
Tao Wang ◽  
...  
Keyword(s):  
Growth Rate ◽  
Elastic Modulus ◽  
Cyclic Loading ◽  
Loading Rate ◽  
Complex Stress ◽  
Stress Conditions ◽  
Energy Evolution ◽  
Plastic Energy ◽  
Damage Process ◽  
Tectonic Coal

It is of great significance to ascertain the mechanical characteristics and deformation laws of tectonic coal that is under complex stress conditions for safe production, but the targeted research in this area is still insufficient at present. This paper performed triaxial tests under cyclic multi-level loading at different rates by using an MTS-815 Rock Mechanics Testing System. The strain characteristics, elastic modulus and energy evolution were obtained in order to explore the effects of the mechanism of loading rate on the evolution of deformation and energy parameters of tectonic coal. The results showed that the irreversible strain and plastic energy increased exponentially with the increase in the deviatoric stress, but the growth rate decreased with the increase in loading rate. Furthermore, the elastic strain increased linearly and the growth rate was essentially unaffected by the loading rate. During the compaction stage, the variation of each parameter was not sensitive to the loading rate; during the elastic and damage stage, the rate increase inhibited secondary defect propagation and improved rock strength. In addition, the stepwise and cumulative energy ratio was defined in order to describe the energy distribution during cyclic loading and unloading. It was found that the decrease in the loading rate was beneficial to the transformation of the total energy into plastic energy. The elastic modulus was the most sensitive to sample damage, but the energy density evolution was able to be used to describe the deformation damage process of tectonic coal in more detail. These findings provide important theoretical support for the tectonic coal deformation law and action mechanism in the damage process that occurs under complex stress conditions.

Low-temperature deformation and strength of alloy steels under complex stress conditions

2010 ◽  
Vol 42 (4) ◽  
pp. 380-386
Author(s):  
A. A. Lebedev ◽  
V. P. Lamashevskii ◽  
I. V. Makovetskii
Keyword(s):  
Low Temperature ◽  
Complex Stress ◽  
Stress Conditions ◽  
Temperature Deformation ◽  
Alloy Steels
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