共查询到20条相似文献,搜索用时 31 毫秒
1.
B. P. Kashyap 《Journal of Materials Science》1991,26(17):4657-4662
Grain growth behaviour of the Al-Cu eutectic alloy was investigated as a function of strain (ε), strain rate
and deformation temperature (T) over
= 10−2 s−1 and T=400 to 540°C. The grain size increases with increase in strain and temperature. Upon deformation to a fixed strain,
the grain growth is generally seen to be more at lower strain rates. The rates of overall grain growth
and due to deformation alone
, however, increase with increasing strain rate according to
and
, respectively. The increase in the grain growth rate with strain rate is attributed primarily to the shorter time involved
at higher strain rate for reaching a fixed strain. The activation energy for grain growth under superplastic conditions is
estimated to be 79 kJ mol−1. 相似文献
2.
New results on the crack-tip fields in an elastic power-law hardening material under plane stress mode I loading are presented.
Using a generalized asymptotic expansion of the stress function, higher-order terms are found which have newly-discovered
characteristics. A series solution is obtained for the elastic-plastic crack-tip fields. The expansion of stress fields contains
both the
and
terms where ti is real and tk is complex; the terms σ(i)
pq(θti) and σ(k)
rsθtk) are real and complex functions of θ respectively. Comparing the results with that for the plane strain mode I loading shows
that: (1) the effect of higher-order solutions on the crack-tip fields is much smaller; and (2) the path-independent integral
J also controls the second-order or third-order term in the asymptotic solutions of the crack-tip fields for most of the engineering
materials (1 < n < 11) in plane stress, while the J-integral does not control the second and the third-order terms for the
plane strain mode I case for n > 3. These theoretical results imply that the crack-tip fields can be well characterized by
the J-integral, and can be used as a criterion for fracture initiation under plane stress mode I loading. This is in agreement
with existing full-field solutions and experimental data that J at crack growth initiation is essentially independent of in-plane
specimen geometry. The comparison confirms the theoretical asymptotic solutions developed in this study.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
O. Ajaja 《Journal of Materials Science》1991,26(24):6599-6605
A model based on the three-dimensional distribution of dislocations is used to delineate the role of recovery during high
temperature constant strain rate deformation. The model provides a good semi-quantitative explanation for classical work-hardening
as well as for high temperature work-softening resulting from rapid recovery. It predicts linear work-hardening, whereby the
ratio of the work-hardening rate,H, to the shear modulus,G, is constant when a crystal is tested in the absence of recovery. The slope of the stress-strain curve, θ, for high temperature
deformation is related to the low temperature work-hardening rateH; the dislocation annihilation rate
, the flow stress a, the free dislocation density ρ, the strain rate
, and a parameter which is sensitive to the dislocation distribution. A modified version of the Bailey-Orowan equation for
simultaneous work-hardening and recovery during constant strain rate deformation which is derived from the model takes the
form
相似文献
4.
Static restoration mechanism during hot interrupted deformation of 304 stainless steel was studied in the temperature range from 900 to 1100°C, various strain rate from 0.05 to 5/sec and pass strain of 0.25–3 times peak strain. It was clarified that the static recrystallization was happened after 3–10 seconds at first deformation. The static restoration was depended on the pass strain, deformation temperature and strain rate and fractional softening (FS) values increased with increasing strain rate, deformation temperature and pass strain. Recystallization kinetics was explained with Avrami equation and Avrami constant was 1.113. This value was independent of deformation variables significantly. The time of 5, 50, 95% recrystallization was evaluated using such equations: t
0.05 = 2.9 × 10–12 –1.17
–0.94
D exp(222000 J/mol/RT), t
0.5 = 2.0 × 10–10 –1.56
–0.81
D exp(197000 J/mol/RT), t
0.95 = 1.9 × 10–8–1.63
–0.76
D exp(173000J/mol/RT). The predicted values by use of upper equations had a good agreement with a measurement. 相似文献
5.
The stress state during “simple” superplastic bulge forming (without a back pressure) is different from that when a back pressure
is applied. In the former procedure, specimens or components are deformed under a biaxial tensile stress state, while in the
latter, the deformation is achieved under the combination of a biaxial tensile stress and a uniaxial compressive stress state.
Both theoretical and experimental studies have shown that when a back pressure is present, the deformation cannot be treated
as simply governed by the difference between the forming pressure and the back pressure. The analytical expressions for the
forming relationships and the influence of back pressure on experimental m-log
(where m is the strain-rate sensitivity and
is the equivalent tensile strain rate for bulge forming) relationships for Zn-22 wt% Al and Zn-4 wt% Al-1% Cu are given.
Results show that with increasing back pressure, the m-log
curve shifted towards higher strain rates, but the maximum m values were not affected. 相似文献
6.
Dispersion-hardened aluminum materials of pure aluminum with extremely fine oxide and carbide dispersions and very fine grain sizes were creep-deformed under compressive loadings between 573 and 773 K. The creep behavior of the investigated materials is influenced by time, temperature, stress level and microstructure. An increasing content of dispersions causes increasing threshold stresses thand resistances against creep. The Norton plots of the minimum creep rate
versus stress are characterized by extremely high stress exponents n. On the basis of the threshold concept it is demonstrated that the same diffusion process dominates in the dispersion-hardened aluminum materials as in pure aluminum. Their true stress exponents n*as the slopes of the best fit lines of the
are close to 5. The threshold stress decreases considerably with increasing temperature due to the thermally activated recovery of long-range internal back stresses of quasi-planar dislocation structures on the grain boundaries. 相似文献
7.
We study the possibility of application of the versions of the theory of sliding [1] with regular and singular loading surfaces
(Σ) under complex loads in the form of two-link paths and establish the relationships between the stress
and strain rates
in a small neighborhood of an angular point in the loading path. The advantages of the theory of sliding with singular surfaces
are discussed and the impossibility of application of the theories of plastic flow with regular surfaces to the solution of
the problems of stability of structural elements is demonstrated. However, their application to the solution of boundary-value
problems of determination of the total strains can be reasonable.
__________
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 2, pp. 10–16, March–April, 2007. 相似文献
8.
A quantum-mechanical analog of the spin-orbit interaction operator
is constructed for the fields of optical CV vortices and TE and TM modes in an optical fiber. It is shown that the polarization
correction δβ to the propagation constant, which is the mean value of this operator, is a measure of the “level splitting” of the propagation
constant
in the scalar case. The difference in the operation of the individual parts of the operator
on the fields of CV vortices and on the fields of TM and TE modes is indicative of the presence of two different physical
processes — circular and linear birefringence in the locally isotropic optical fiber. The conversion of the “scalar” field
to a vector field e
1 as a consequence of the spin-orbit interaction operator can be regarded as resulting from a re-radiation of the additional
field e
1 by the vortex field
, which rotates around the optical axis of the fiber. In this picture the additional field e
1 can be regarded as being a “relativistic” correction to the vortex field for the distortions of the main field
and arising as a result of the rotation of the field of the optical vortex in the medium of the few-mode fiber.
Zh. Tekh. Fiz. 24, 87–93 (October 26, 1998) 相似文献
9.
The relation between vacancy concentration, C
v and tensile plastic strain, ɛ, has been constantly expressed as C
v ∞ ɛ
m
. To take into account the grain-size effect, we have recently proposed that C∞ ɛβv ∞ϱm, where ϱm is the mobile dislocation density. With the conventional expression that ϱm
d
−n
, where d is the average grain size, the strain and grain-size dependence of vacancy concentration appears to be C
v ∞ ɛβγ
d
-nγ. This equation has proved effective in rationalizing the onset strain, ɛc, and stress amplitude, Δσ, of flow instability associated with the Portevin-LeChatelier effect of substitutional f c c alloys,
where ɛc and Δσ are described by
|
设为首页 | 免责声明 | 关于勤云 | 加入收藏 |
Copyright©北京勤云科技发展有限公司 京ICP备09084417号 |