A model of thermomechanical fatigue in a lead-base alloy

1993 ◽  
Vol 8 (4) ◽  
pp. 745-756 ◽  
Author(s):  
Larry Lawson
Keyword(s):  
Grain Boundary ◽  
Crack Growth ◽  
Oxide Layer ◽  
Single Phase ◽  
Base Alloy ◽  
Crack Tip ◽  
Thermomechanical Fatigue ◽  
Boundary Crack ◽  
Fcc Metal ◽  
Good Agreement

A model for the growth of a grain boundary crack in thermomechanical fatigue is derived for a single-phase or low alloy fcc metal at homologous temperatures near 0.5. Crack growth is hypothesized to proceed through vacancies binding in pairs at the crack tip to impurities or an oxide layer. This model is applied to 97Pb−3Sn, and the results compared with experiment. Good agreement is shown between the model and experiment, especially in predicting the effects of frequency and thermal-mechanical phasing. These effects do not appear to have been previously modeled successfully.

scholarly journals Influence of Grain Boundary on the Fatigue Crack Growth of 7050-T7451 Aluminum Alloy Based on Small Time Scale Method

2016 ◽  
Vol 2016 ◽  
pp. 1-7 ◽  
Author(s):  
Weihan Wang ◽  
Weifang Zhang ◽  
Hongxun Wang ◽  
Xiaoliang Fang ◽  
Xiaobei Liang
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Grain Boundary ◽  
Crack Growth ◽  
Time Scale ◽  
Crack Tip ◽  
Fatigue Loading ◽  
Small Time ◽  
Scale Method

Based on the small time scale method, the influence of grain boundary on the fatigue crack growth of 7050-T7451 has been investigated. The interaction between fatigue crack and grain boundary was investigated by in situ SEM testing. Results showed that the fatigue crack growth will be retarded by grain boundary when the angle between fatigue crack and grain boundary is greater than 90 degrees. Mechanism analysis showed that the fatigue crack tip would not be able to open until the loading reached the 55% of maximum load, and the fatigue crack had been closed completely before the loading was not reduced to the minimum value, which led to the crack growth retardation. When the 7050-T7451 aluminum alloy suffered from fatigue loading with constant amplitude, a behavior of unstable fatigue crack growth could be observed often, and results indicated that the bridge linked mechanism led to the behavior. The grain boundary was prone to fracture during fatigue loading, and it became the best path for the fatigue crack growth. The fatigue crack tip would be connected with fractured grain boundary eventually, which led to the fast crack growth in different loading stage.

Coupled effect of grain boundary sliding and dislocation emission on fracture toughness of nanocrystalline materials

2016 ◽  
Vol 01 (02) ◽  
pp. 1650008 ◽  
Author(s):  
Q. H. Fang ◽  
L. C. Zhang
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Crack Growth ◽  
Nanocrystalline Materials ◽  
Crack Tip ◽  
Grain Boundary Sliding ◽  
Dislocation Emission ◽  
Disclination Dipole ◽  
Coupled Effect ◽  
Wedge Disclination

This paper establishes a theoretical model to explore the coupled effect of grain boundary (GB) sliding deformation and crack tip dislocation emission on the critical stress intensity factor (SIF) for crack growth in ultrafine-grained and nanocrystalline materials (NCMs). The model postulates that the stress concentration near a crack tip initiates GB sliding. It is found that GB sliding leads to the formation of wedge disclination dipole at the triple junctions of grain boundaries. Under the external load and stress fields produced by wedge disclinations, dislocations are emitted from crack tips but will stop at the opposite GBs. The influence of the wedge disclination dipole and the dislocation emitted from crack tip on the critical SIF for crack growth is investigated. The model prediction shows that the critical SIF varies with the decrement of grain size, and that there is a critical grain size corresponding to a minimum value of SIF. Compared with the pure brittle fracture in NCMs at the grain sizes of tens of nanometers, the combined deformation mechanisms can bring an increase of the critical SIF for crack growth.

Validation of the K and J Parameters in a Compact Tension Specimen Containing Intergranular and Straight Crack Paths

2010 ◽  
Author(s):  
A. N. Mehmanparast ◽  
C. M. Davies ◽  
K. M. Nikbin
Keyword(s):  
Finite Element ◽  
Grain Boundary ◽  
Crack Growth ◽  
Crack Tip ◽  
Compact Tension ◽  
Growth Direction ◽  
Compact Tension Specimen ◽  
Contour Integral ◽  
Transgranular Crack ◽  
Crack Profile

Methods have been examined to evaluate the fracture mechanics parameters J and K in finite element (FE) analyses on a compact tension, C(T), geometry using a mesh appropriate for the evaluation of both intergranular and transgranular microstructural damage processes. Realistic grain and grain boundary microstructures were modelled using ABAQUS. Both straight and deviating crack profiles were considered, representing transgranular and intergranular crack growth processes, respectively. Elastic and elastic-plastic finite element analyses were performed on a C(T) specimen model with a standard straight and deviating crack profile to derive and compare the stress intensity factor, K, and J parameter values under plane stress and plane strain conditions. Considerations as to the validity of the J domain integral calculations that ABAQUS computes are discussed. It has been found that the values of K and J obtained from FE simulations are consistent with theoretical solutions and the stress distribution ahead of the crack tip is very close to that of expected from analytical studies for the case of a straight fronted transgranular crack. Reasonable values of K and J parameters could also be achieved from the FE contour integral values of a deviating crack when the contours selected were adequately far from the crack tip. However, significant differences were found between the analytical and FE contour integral values of a deviating crack when the crack growth direction was considered to continue at the angle defined by its grain boundary. The values of J obtained by from the load line displacement measurements were uninfluenced by the crack profile and in good agreement with other analytical solutions.

Grain boundary crack growth in metastable titanium β alloys

2015 ◽  
Vol 82 ◽  
pp. 167-178 ◽  
Author(s):  
S. Osovski ◽  
A. Srivastava ◽  
J.C. Williams ◽  
A. Needleman
Keyword(s):  
Grain Boundary ◽  
Crack Growth ◽  
Boundary Crack

Grain boundary crack growth in interconnects with an electric current

2001 ◽  
Vol 86 (2) ◽  
pp. 101-108 ◽  
Author(s):  
Chao-Yuan Liu ◽  
Sanboh Lee ◽  
Tze-jer Chuang
Keyword(s):  
Grain Boundary ◽  
Electric Current ◽  
Crack Growth ◽  
Boundary Crack

A more Accurate Constraint Parameter to Characterize the Creep Constraint Effect at Crack Tip of Cr-Mo-V Steel

2019 ◽  
Vol 795 ◽  
pp. 79-85
Author(s):  
Yun Luo ◽  
Qian Zhang ◽  
Wen Chun Jiang
Keyword(s):  
Experimental Data ◽  
Crack Growth ◽  
Rate Equation ◽  
Crack Tip ◽  
Growth Data ◽  
Constraint Effect ◽  
Creep Time ◽  
Brazed Joint ◽  
Crack Tip Constraint ◽  
Good Agreement

A suitable constraint parameter is a key to quantify the creep crack tip constraint levels. In this study, a new more accurate creep constraint parameter As of brazed joint was proposed based on the existing constraint parameters R* and Ac. The CCG rate equation of Cr-Mo-V steel related to the constraint parameter As is obtained. The results show that the constraint parameter As is basically unchanged with the increase of creep time. The crack growth data predicted by the constraint dependent CCG rate equation are in good agreement with the experimental data. The established constraint dependent CCG rate equation can predict the CCG rate at other constraint levels very well.

Examination of Fracture Interfaces in Silicon Nitride

1975 ◽  
Vol 33 ◽  
pp. 60-61
Author(s):  
Nancy J. Tighe
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Slow Crack Growth ◽  
Ceramic Materials ◽  
Grain Boundary Sliding ◽  
Boundary Phase ◽  
Turbine Engines ◽  
Boundary Sliding

Silicon nitride is one of the ceramic materials being considered for the components in gas turbine engines which will be exposed to temperatures of 1000 to 1400°C. Test specimens from hot-pressed billets exhibit flexural strengths of approximately 50 MN/m2 at 1000°C. However, the strength degrades rapidly to less than 20 MN/m2 at 1400°C. The strength degradition is attributed to subcritical crack growth phenomena evidenced by a stress rate dependence of the flexural strength and the stress intensity factor. This phenomena is termed slow crack growth and is associated with the onset of plastic deformation at the crack tip. Lange attributed the subcritical crack growth tb a glassy silicate grain boundary phase which decreased in viscosity with increased temperature and permitted a form of grain boundary sliding to occur.

COMPUTER MODELING OF CHEMICAL EQUILIBRIUMS IN WO3–H2O SYSTEM

2017 ◽  
pp. 35-48 ◽  
Author(s):  
V.P. Bondarenko ◽  
O.O. Matviichuk
Keyword(s):  
Transition Temperature ◽  
Gas Phase ◽  
Single Phase ◽  
Reference Data ◽  
Maximum Amount ◽  
Reaction Products ◽  
Influence Of Temperature ◽  
Equilibrium Chemical ◽  
Program Data ◽  
Good Agreement

Detail investigation of equilibrium chemical reactions in WO3–H2O system using computer program FacktSage with the aim to establish influence of temperature and quantity of water on formation of compounds of H2WO4 and WO2(OH)2 as well as concomitant them compounds, evaporation products, decomposition and dissociation, that are contained in the program data base were carried out. Calculations in the temperature range from 100 to 3000 °С were carried out. The amount moles of water added to 1 mole of WO3 was varied from 0 to 27. It is found that the obtained data by the melting and evaporation temperatures of single-phase WO3 are in good agreement with the reference data and provide additionally detailed information on the composition of the gas phase. It was shown that under heating of 1 mole single-phase WO3 up to 3000 °С the predominant oxide that exist in gaseous phase is (WO3)2. Reactions of it formation from other oxides ((WO3)3 and (WO3)4) were proposed. It was established that compound H2WO4 is stable and it is decomposed on WO3 and H2O under 121 °C. Tungsten Oxide Hydrate WO2(OH)2 first appears under 400 °С and exists up to 3000 °С. Increasing quantity of Н2О in system leads to decreasing transition temperature of WO3 into both liquid and gaseous phases. It was established that adding to 1 mole WO3 26 mole H2O maximum amount (0,9044–0,9171 mole) WO2(OH)2 under temperatures 1400–1600 °С can be obtained, wherein the melting stage of WO3 is omitted. Obtained data also allowed to state that that from 121 till 400 °С WO3–Н2O the section in the О–W–H ternary system is partially quasi-binary because under these temperatures in the system only WO3 and Н2O are present. Under higher temperatures WO3–Н2O section becomes not quasi-binary since in the reaction products WO3 with Н2O except WO3 and Н2O, there are significant amounts of WO2(OH)2, (WO3)2, (WO3)3, (WO3)4 and a small amount of atoms and other compounds. Bibl. 12, Fig. 6, Tab. 5.

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