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1.
The value of the J-integral at the onset of crack extension from a weld defect: Weld material is softer than parent material 总被引:3,自引:0,他引:3
E. Smith 《International Journal of Fracture》1992,53(1):33-42
The paper addresses the problem of crack extension in a weld in an engineering structure for the case where the weld crack is parallel to the plane of the weld, a situation for which the J-integral is path independent with regard to any contour surrounding a crack tip. Assuming that crack extension is associated with the attainment of a critical crack tip opening displacement w, a theoretical analysis based on the strip yield representation of plastic deformation shows, for the case where the weld material is softer than the parent material, how the relation between the value of J at the onset of crack extension and w depends on the flow properties of the weld and parent materials, the crack size and the weld thickness. 相似文献
2.
The rate/temperature dependent fracture behaviour of plain and glass-filled polystyrene has been investigated over the crack speed (a) range of 10–6 to 10–2 m sec–1 and in the temperature (T) range of 296 to 363 K. TheK
c (a, T) relationships obtained, whereK
c is the stress intensity factor at fracture, are shown to follow those given by the Williams/Marshall relaxation crack growth model and the toughness-biased rate theory. Crack propagation in both materials is shown to be controlled by a-relaxation molecular process associated with crazing. Crack instabilities observed in plain polystyrene are analysed successfully in terms of isothermal-adiabatic transitions at the crack tip. Fracture initiation experiments are also conducted in which the effects of organic liquids on the fracture resistances of both plain/glass-filled polystyrene have been determined. Good correlations betweenK
i
2
(K
i being the crack initiation stress intensity factor) and s, solvent solubility parameter, of various liquid environments have been obtained, which give a minimumK
i
2
value at s p, where p is the solubility parameter of the polymer. For a given temperature, liquid environment and crack speed, the glass-filled polystyrene is shown to possess greater resistances to crack propagation than plain polystyrene. 相似文献
3.
We propose an experimental-theoretical engineering procedure for assessing the strength of butt-welded joints using the force (KIc) and strain (c) criteria of the brittle and quasibrittle fracture mechanics, respectively. For this purpose, beam specimens with square and bevel welds and an initial edge crack or notch in the weld metal are tested under three-point bending. The parameter KImax controlling fracture of a bent beam with an inclined (Mode I + Mode II) crack is assessed taking into account the values of the stress intensity factors KI and KII, and the crack inclination angle *. We also studied the plastic zone at the crack tip and the crack propagation kinetics depending on the weld geometry and the V-notch tip radius for butt-welded joints. The data obtained allow one to rate such joints by their strength according to the fracture toughness criteria KIc and c. 相似文献
4.
A transferability model for brittle fracture including constraint and ductile tearing effects: a probabilistic approach 总被引:1,自引:0,他引:1
This study describes a computational framework to quantify the influence of constraint loss and ductile tearing on the cleavage fracture process, as reflected by the pronounced effects on macroscopic toughness (J
c , c). Our approach adopts the Weibull stress w as a suitable near-tip parameter to describe the coupling of remote loading with a micromechanics model incorporating the statistics of microcracks (weakest link philosophy). Unstable crack propagation (cleavage) occurs at a critical value of w which may be attained prior to, or following, some amount of stable, ductile crack extension. A central feature of our framework focuses on the realistic numerical modeling of ductile crack growth using the computational cell methodology to define the evolution of near-tip stress fields during crack extension. Under increased remote loading (J), development of the Weibull stress reflects the potentially strong variations of near-tip stress fields due to the interacting effects of constraint loss and ductile crack extension. Computational results are discussed for well-contained plasticity, where the near-tip fields for a stationary and a growing crack are generated with a modified boundary layer (MBL) formulation (in the form of different levels of applied T-stress). These analyses demonstrate clearly the dependence of w on crack-tip stress triaxiality and crack growth. The paper concludes with an application of the micromechanics model to predict the measured geometry and ductile tearing effects on the cleavage fracture toughness J
c of an HSLA steel. Here, we employ the concept of the Dodds-Anderson scaling model, but replace their original local criterion based on the equivalence of near-tip stressed volumes by attainment of a critical value of the Weibull stress. For this application, the proposed approach successfully predicts the combined effects of loss of constraint and crack growth on measured J
c -values. 相似文献
5.
We construct a numerical model of subcritical growth of cracks in metals subjected to the simultaneous action of loading and corrosive hydrogen-containing media. The model is based on the hypothesis that hydrogen plays the predominant role, that under the conditions of stress corrosion, the process of crack growth passes through two stages, and on the deformation criterion of fracture. The crack-growth rate was determined as a function of the crack tip opening displacement , its critical value c, standard electrode potential of the metalE
0, and pH value of the medium. The reliability of the model under consideration is corroborated by experimental results.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 2, pp. 68–74, March – April, 1995. 相似文献
6.
The chemical control of underdoped and overdoped states in the Y(Ba2 – y
Sr
y
)Cu3O6 + (0.1 and 0.9) compounds has been observed by high-resolution O K-edge X-ray-absorption near-edge-structure spectra. The chemical substitution of Sr for Ba in the fully-oxygenated Y(Ba2–y
Sr
y
)Cu3O6 + (0.9) compounds gives rise to high hole concentrations within both the CuO2 planes and the out-of-plane sites, leading to the overdoped state and the decrease in the superconducting transition temperature from 92 K for y=0 to 84 K for y=0.8. In contrast, an increase in the Sr content in the oxygen-deficient Y(Ba2 – y
Sr
y
)Cu3O6 + (0.1) compounds did not indicate superconductivity. The oxygen-deficient compounds exhibit the underdoped state due to the low hole concentration. 相似文献
7.
Combined processing of YBa2Cu3O7-δ superconducting wire by mechanical work and melt growth technique
Jung-Ho Ahn Kook-Hyun Ha Hyungsik Chung 《Journal of Materials Science: Materials in Electronics》1991,2(2):94-97
The combination of mechanical work by powder-in-tube processing and melt growth of YBa2Cu3O7- was investigated. During the heat treatment of Ag-sheathed YBa2Cu3O7- wire above the melting point of Ag, the sheath was melted and removed from the superconducting wire, but a small portion of Ag infiltrated into the core. Mechanical working before the heat treatment is beneficial for improvingJ
c. Heat treatments above 1015°C resulted in higherJ
c values for drawn wires than the samples without mechanical working. A proper combination of mechanical working and melt growth appears very promising for making high-J
c wire with good strength. 相似文献
8.
The flexural strengths of rectangular YBa2Cu3O6+ bars, prepared from mixed oxides and carbonates or spray-dried precursors, have been measured at room temperature and at 77 K. Strengths ranged from 17.8 to 57.6 M Pa at room temperature, depending on processing history, and were 20% greater when measured at 77 K. Corrosion of YBa2Cu3O6+ in humid air at 38° C created two layers of corrosion products, but did not weaken the uncorroded core when failure loads were corrected for the decreased sample dimensions. The Knoop hardness of polycrystalline YBa2Cu3O6+ ranged from 436 to 447 KHN while the hardness of individual grains of YBa2Cu3O6+ was 498 KHN. Variations in flexural strength with microstructure were observed and are discussed. 相似文献
9.
B. Holzapfel M. Leghissa P. Bauer G. Kreiselmeyer M. Kraus S. Bouffard L. Schultz G. Saemann-Ischenko 《Journal of Superconductivity》1994,7(1):205-207
Epitaxial YBa2Cu3O7–
thin films (YBCO) and YBa2Cu3O7–
/PrBa2Cu3O7–
multilayers (Y/Pr) were irradiated with high-energy heavy ions (770 Mev208Pb) under various directions relative to thec-axis. The irradiation resulted in columnar defects tilted by from thec-axis. The angular dependence of their pinning activity was studied by measuring the anisotropy of the critical current density. TheJ
c
(B, T,) behavior of the irradiated YBCO thin films showed an additional peak, which exceeds the intrinsic pinning peak, exactly at the irradiation direction. The Y/Pr multilayers, however, showed an isotropicT
c
-enhancement by a factor of 5, without any additional structure in theJ
c(B, T,) curve. 相似文献
10.
Sha Jiangbo Sun Jun Zuh Pin Deng Zengjie Zhou Huijui 《International Journal of Fracture》2000,104(4):409-423
In this paper, the relationship between the J-integral and COD under mixed mode I+II loading was proposed and investigated. The J-integral was calculated by the Finite Element Method, and COD was defined by Rice`s model and measured by a duplicating method in an aluminum alloy Ly12. The critical values of the J-integral and COD for a stable mixed crack initiation were also determined by a resistance curve. It shows that: (1) the mixed J-integral, J
M, and the mixed COD satisfy the relations of J
M=dn0CTOD+ds0CTSD and J
M=dyieldCOD, where dn, ds and d are coefficients; CTOD and CTSD are the mode I and mode II components of COD, respectively; 0 and 0 are the tensile and shear stresses at the crack tip strip, respectively, and (2) the initiation values of the J-integral and COD of mixed stable crack growth increase with an increasing mode II component, the J
IIC value is 2 times greater than that of J
IC, and the CODi for a pure mode II crack is 6 times greater than that of CODi for a pure mode I crack. 相似文献
11.
The propagation of blunt notches in stainless steel has been studied experimentally and analysed using generalized fracture mechanics (GFM), which takes account of inelastic and non-linear deformation. According to this theory, the critical apparent energy release rate, which is equivalent toJ
c, is given byJ
c=k
1 (0)cW
0c for an edge crack of lengthc in a thin sheet (plane stress), wherek
1 (0) is a dimensionless function of strain, 0, andW
0c is the input energy density remote from the crack at the time of crack propagation. The validity of this equation was demonstrated for blunt cracks and the functionk
1 (0) evaluated. The value ofJ
c was measured for blunt cracks of different lengths and tip diameters, and also for different crack extensions.J
c was found to be independent of crack length for the smallest tip radius, but became systematically length-dependent as the radius increased. However, the dependence ofJ
c on crack length, tip radius and crack extension can be expressed by a single empirical function, as is suggested by GFM. The propagation of cracks from blunt notches in ductile materials can, therefore, be handled by fracture mechanics methods. 相似文献
12.
The oxalate precursor yielded by a sol-gel processing can be pyrolysed and oxidized at 840 ° C for 40h into the desired high-T
c superconductor in the lead-doped Bi-Sr-Ca-Cu-O system withT
c(onset) = 140 K andT
c(zero) = 104K. The mechanisms of the sol-gel reaction were monitored by analysis of Fourier transformation infrared (FTIR) spectroscopy. Moreover, identification of the various phases existing on the specimens after firing at selected temperatures, was made by analysis by FTIR spectroscopy and X-ray diffractometry. Based on the experiment results, the mechanisms of forming Bi2Sr2CaCu2O8+ (phase 2212) might be identified as the reaction of Bi2Sr2CuO6+, Ca2CuO3 and CuO at 800 ° C. Furthermore, Bi2Sr2Ca2Cu3O10+ (phase 2223) might be synthesized by the reaction of phase 2212, Ca2CuO3 and CuO at 840 ° C. Ca2PbO4 found in lead-doped materials may catalyse the formation reaction of Ca2CuO3 at 650 ° C and play a role of a flux to fuse Bi2Sr2CaCu2O8+, CuO and residual Ca2CuO3 and then improve the further synthesis of Bi2Sr2Ca2Cu3O10+ at 840 C. 相似文献
13.
The results are presented of experimental examination of the displacement of the edges of a separation crack in brittle (silicated glass) and quasi-brittle (polymethyl methacrylate) materials deformed in uniaxial static loading in tension, compression, and bending (eccentric tension). The results of analysis of these data are used to introduce the new interpretation of various basic concepts, such as the end region of the crack d, opening displacement 1 and the crack tip opening 1. It is attempted to obtain values of the strain parameters d, 1 1, invariant to the method of determination. These values correspond to the start of crack propagation in the examined materials. It is shown that the quantities Ii in brittle failure and Ii in quasi-brittle failure are relatively independent of the type of tested specimen.Translated from Problemy Prochnosti, No. 10, pp. 25–31, October, 1991. 相似文献
14.
Y. W. Mai 《Journal of Materials Science》1976,11(2):303-316
The effects of organic liquid environments on the fracture behaviour of acrylonitrile-butadiene-styrene (ABS) have been investigated. Fracture initiation experiments showed thatK
i
2
, (K
i being the stress intensity factor at crack/craze initiation), could be meaningfully correlated with the solvent solubility parameter (
s) of the different liquid environments and had a minimum value at
s=
p, where
p was the solubility parameter of ABS. For the range of organic liquids used, hydrogen bonding did not have any significant effects on the correlations. It was demonstrated that theK
i
2
–
s correlations could also be usefully extended to other materials such as plain and glass-filled polystyrenes. At a common crack speed (å), the fracture toughness (R) values in crazing liquids (i.e. alcohols) were greater than those in cracking solvents (i.e. acetone, benzene, toluene, etc.) which usually caused a dissolution effect on the plastic. From crack propagation experiments, and using fracture mechanics analyses, definiteR(å) andK
c(å) relationships for ABS immersed in toluene, carbon tetrachloride and methanol were determined. These experimental results showed that crack propagation was relaxation controlled and agreed well with a recent theoretical analysis due to Williams and Marshall for environmental crack and craze growth in polymers. Finally, SEM pictures were presented to show the remarkable differences in the fracture morphologies of ABS in both crazing and cracking liquid environments. 相似文献
15.
F. Minami A. Brückner-Foit D. Munz B. Trolldenier 《International Journal of Fracture》1992,54(3):197-210
The local approach was recently proposed by Beremin and Mudry for evaluating the statistical behaviour of toughness results of materials. This approach introduces a stress parameter
w
, termed the Weibull stress, as a measure of the fracture resistance of materials instead of the conventional toughness parameters such as K
c,
c
and J
cl (critical stress intensity factor, CTOD and J-integral, respectively). The Weibull stress
w
obeys the Weibull distribution with the two parameters m and
u
(the shape and the scale parameter, respectively). The first parameter m is normally estimated to be 22 irrespective of the kind of material. In this paper a procedure for the determination of the Weibull parameters m and
u
is developed. This procedure consists of the determination of the plastic zone ahead of the crack tip, from which cleavage fracture originates, and of the maximum likelihood estimation of the parameters m and
u
based on the stress distribution in the plastic zone. Calculations using this procedure confirm that the distribution of the Weibull stress
w
is a material property independent of specimen thickness, and in particular that the shape parameter m depends on the material, e.g. m12 for a German reactor pressure vessel steel (20 Mn Mo Ni 5 5). Using these parameters for the distribution of the Weibull stress the size effect in fracture toughness values is predicted and an improved agreement between theory and experiments is obtained compared to the Weakest Link model. 相似文献
16.
The non-linear creep behaviour has been studied on PET films at room temperature. A particular value of the stress, c, was used to characterize the change between the linear to the non-linear domain. The variations of the elastic modulus, the relaxed modulus and c revealed great sensitivity to the morphology of the crystallization. A molecular model of non elastic deformation, assuming (i) hierarchical correlated molecular motion, and (ii) nucleation and expansion of sheared-microdomains, was used to analyse the role of stress on anelasticity. To take into account the two-phase structure of semicrystalline films, a phenomenological series/parallel model was applied to express the mechanical coupling between amorphous and crystalline phases. Quantitative agreement was found between theoretical predictions and experimental data for low and high stresses. However, there was a discrepancy in the rate of recovery because the model predicts a strain recovery slower than the experimental behaviour. Consequently, it is proposed to develop further the molecular model mentioned above by specifying the energy profile of a sheared-microdomain and its stress dependence. Then, the difference between creep and recovery strain rate could be explained.Nomenclature
A
Anelastic equilibrium compliance
-
A
Parameter proportional to the relaxation strength
-
b
Shear vector
-
Correlation parameter
-
i
Particular value in the distribution
-
e
Average value in the material ( = 0.27)
-
Correlation parameter characterizing the ability of chain orientation
-
d
a
Amorphous density
-
d
c
Crystalline density
-
Parameter of the mechanical mixing law
-
E
Tensile modulus
-
E
c
Crystalline Young's modulus
-
g
i
Statistical weight in the distribution
-
G
0
Shear modulus at 0 K
-
J
max
Creep compliance at the end of the creep time
-
J
max(0)
Value ofJ
max for low stresses
-
J
u
Unrelaxed compliance
-
J
i(
i;A
i)
Calculated compliance for a couple (
i;A
i)
-
J
exp
Experimental creep compliance
-
J
a
Compliance of the amorphous part
-
J
c
Compliance of the crystalline part
-
J
sc
Compliance of the semi-crystalline material
-
k
Boltzmann's constant
-
Parameter of the mechanical coupling law
-
R
Radius of a shear micro domain
- 0
Stress necessary to cross the energy barrier only by mechanical activation
-
T
c
Crystallization temperature
-
t
c
Creep time
- mol
Time for a translational motion of a structural unit over a distance comparable to its size
-
Particular value of mol in the time distribution
-
Characteristic time for the secondary relaxation
- 0
Time proportional to the Debye time
-
t
0
Scaling time parameter determined by the experimental value of mol
-
U
Activation energy for an elementary molecular motion
-
X
c
Crystallinity ratio
-
V
a
Volume fraction of the amorphous part
-
V
c
Volume fraction of the crystalline part 相似文献
17.
Sean Songbai Ji Guy M. Genin Paul C. Paris Thomas R. Berkel Alex M. Rubin 《International Journal of Fracture》2004,129(1):63-73
This paper establishes a simple testing scheme to simultaneously measure the linear elastic strain energy release rate G, the non-linear J-integral, and the rate-dependent C
*-integral for a growing crack at a polymer/metal interface. The test is applicable to fracture of adhesive bonds. A criterion governing C
*-controlled fracturing is derived, analogous to the Hutchinson-Paris -criterion for J-controlled growth. The interfacial toughness of an adhesive commonly used for bonding metal plates is characterized at room temperature, and is shown to fracture in a C
*-controlled manner. A relationship between C
* and the crack growth rate is observed. The nature of this relationship warrants further exploration. 相似文献
18.
The dependence of the zero temperature gap to the critical temperature for s- and d-wave superconductors on the Fermi level shift () from the Van Hove singularity is studied within the BCS theory. Exact numerical calculations for the s and d gap ratios are carried out and approximate analytic expressions for the ratio are given. We find that the maximum gap ratio occurs at = 0 and it decreases slowly with increasing , and that this behavior is symmetric with respect to . 相似文献
19.
Phases, microstructures and properties of lead-zirconate-titanate (PZT) ceramics with the compositions Pb(Zr0.535– Ce Ti0.465) O3 where =0.0, 0.001, 0.01, 0.02 and 0.05 were studied. Rhombohedral and tetragonal phases were present at =0.0. The amount of the rhombohedral phase increased with increasing , and only the tetragonal phase was present for >0.001. Thec/a ratio of the tetragonal phase also increases with increasing . Particles of CeO2 were found to be present in compositions with >0.01, indicating that the solubility of CeO2 is less than 1a/o on the metals basis. The piezoelectric and electromechanical constants achieved maximum values for =0.001. The hardness increased monotonically with increasing . The modulus of rupture and the fracture toughness, however, went through a minimum and both stayed lower than their values for =0. 相似文献
20.
V. M. Shapovalov N. V. Tyabin S. K. Ivashchenko 《Journal of Engineering Physics and Thermophysics》1979,37(5):1322-1325
A mathematical model is obtained for the process of cooling with formation of a planar film. The solution obtained is verified experimentally.Notation
mean axial velocity gradient
- vx
current axial velocity
- vo
initial polymer velocity
- v1
sampling velocity
- K
draw ratio
-
deformation rate tensor
- x, y, z
spatial coordinates
- X, Y
dimensionless coordinates
- L()
differential operator
- T
temperature
- To
initial temperature
- Tc
temperature of surrounding medium
-
dimensionless temperature
-
dimensionless temperature averaged over film thickness
-
thermal-diffusivity coefficient
- 2o
initial film thickness
-
thermal conductivity
-
heat-transfer coefficient
- f(X)
distance function
- Bi
Biot criterion, Bio, Biot criterion calculated for initial film thickness
- Gz*
modified Graetz criterion
- V
dimensionless velocity
- 1, 2, 3
heat-transfer coefficients produced by radiation, free convection, and forced convection
- vc, c
mean velocity and film half-thickness in formation zone
- T1
calculated temperature value
- T2
experimental temperature value
-
l
formation zone length
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 5, pp. 854–858, November, 1979. 相似文献