共查询到20条相似文献，搜索用时 46 毫秒
1.
The stress-intensity factor (SIF) of the semi-elliptical surface crack in the finite body under extensional stress is sclculated
by using the FEM software ANSYS release 5.5. The correction factor M
f of SIF at different point along the front of the crack is determined. The relation between M
f and the semi-elliptical shape a/c, the relative crack depth a/b, the variation of angle ϑ, the relative crack width 2c/w and the relative height-width ratio h/w are calculated respectively. Finally the application range and the modification of the engineering formula about SIF is proposed. 相似文献
2.
This paper discusses stress intensity factor (SIF) calculations for surface cracks in round bars subjected to combined torsion
and bending loadings. Different crack aspect ratios, a/b, ranging from 0.0 to 1.2 and relative crack depths, a/D, ranging from 0.1 to 0.6 were considered. Since the loading was non-symmetrical for torsion loadings, a whole finite element
model was constructed. Then, the individual and combined bending and torsion loadings were remotely applied to the model.
The equivalent SIF method, F*EQ, was then used explicitly to combine the individual SIFs from the bending and torsion loadings. A comparison was then carried
out with the combined SIF, F*FE, obtained using the finite element analysis (FEA) under similar loadings. It was found that the equivalent SIF method successfully
predicted the combined SIF for Mode I. However, discrepancies between the results determined from the different approaches
occurred when F
III was involved. It was also noted that the predicted F*FE using FEA was higher than the F*EQ predicted through the equivalent SIF method due to the difference in crack face interactions. 相似文献
3.
利用自主研制的大型土工试验装置,在考虑桩长和桩尖角度影响的情况下,开展了静压桩的沉桩以及静载荷试验,以研究试验过程中桩端阻力的变化规律。试验结果表明:沉桩过程中,桩端阻力随沉桩深度的增加而非线性增大,也随桩长和桩尖角度的增加而增大,沉桩深度为25D时,桩端阻力基本达到极值,同一沉桩深度处桩端阻力在沉桩阻力中的占比随桩长(20D~30D范围内)的增加而减小,随桩尖角度的增加而增大;静载荷试验过程中,桩端阻力随沉降量的增加而非线性增大,也随桩长和桩尖角度的增加而增大,同一沉降量处桩端阻力在桩顶荷载中的占比随桩长的增加而减小,随桩尖角度的增加而增大。 相似文献
4.
This paper introduces a formula for the vertical pressure on a buried pipeline by using a modification of the basic assumptions
of Marston’s theory. The fill’s cohesion is considered. The included angle between the slide surface above the pipeline and
the horizontal surface is assumed to be equal to the fill’s angle of friction. The friction is calculated by multiplying the
active earth pressure on the outer column and the coefficient of the friction on the slide planes It was found that the fill’s
cohesion had important influence on the vertical pressure, whose vertical pressureC
c decreases with increase of the fill depth, a relationship according with that observed in practice. At the end of the paper,
the formula is employed to analyze a practical case.
Project (No. RC9609) supported by Natural Science Foundation of China (NSFC) 相似文献
5.
The flat dilatometer test (DMT) has the potential to be a useful tool in the evaluation of liquefaction potential of soils.
In practice, it is necessary to carefully examine existing DMT-based methods for evaluating liquefaction potential. We conducted
the DMT and cone penetration test (CPT) in high liquefaction potential areas to examine the existing DMT-based methods for
liquefaction potential evaluation. Specifically, the DMT and CPT were conducted side-by-side at each of six in-situ sites,
and thus it is feasible to utilize those test results to validate the existing DMT-based methods. The DMT parameter, horizontal
stress index (K
D), is used as an indicator for estimating liquefaction resistance of soils in terms of cyclic resistance ratio (CRR). The
analysis results revealed that the existing K
D-based liquefaction evaluation methods would overestimate the CRR of soils, which leads to overestimation of the factor of
safety against liquefaction. Also, the estimations of DMT-K
D values by using the CPT-q
c as well as the correlation between DMT-K
D and CPT-q
c proposed by the previous studies would be significantly smaller than field measurements. The results reflected that further
validation of the existing DMT-based methods for liquefaction evaluation is desirable. 相似文献
6.
1 Ｉｎｔｒｏｄｕｃｔｉｏｎ Ｆｅ Ｎｉａｌｌｏｙｉｓｗｉｄｅｌｙｕｓｅｄａｓｓｏｆｔｍａｇｎｅｔｉｃｍａｔｅｒｉａｌｓｆｏｒａｌｏｎｇｔｉｍｅ .Ｉｔｓｍａｇｎｅｔｉｃｐｒｏｐｅｒｔｉｅｓａｓｉｎｉｔｉａｌｐｅｒｍｅ ａｂｉｌｉｔｙμｉａｎｄｃｏｅｒｃｉｖｉｔｙｆｏｒｃｅＨｃｄｅｐｅｎｄｓｔｒｏｎｇｌｙｏｎｔｈｅｃｈｅｍｉｃａｌｃｏｍｐｏｓｉｔｉｏｎａｎｄｔｒｅａｔｍｅｎｔｌｉｋｅｑｕｅｎｃｈｉｎｇｆｒｏｍｈｉｇｈｔｅｍｐｅｒａｔｕｒｅ .Ａｓｕｌｔｒａｆｉｎｅｐａｒｔｉｃｌｅｉｓｒｅｖｅａｌｅｄｒ… 相似文献
7.
采用MP-PIC (multi-phase particle in cell)方法模拟了三维多段气化炉（上部快速床,下部鼓泡床）多粒径煤粉的循环流化过程,研究了分布板不同进气方向对气化炉内颗粒分布的影响。结果表明:分布板开孔与水平方向夹角越大,物料进入快速床并形成流化状态越快,但对成形后的流化形态影响较小;分布板进气方向对分布板处的轴向颗粒浓度分布影响较大,对快速床内轴向颗粒浓度分布影响较小;随着分布板进气方向与水平夹角的减小,鼓泡床下部颗粒浓度增大,固相颗粒通量增大;分布板进气方向对旋风分离效率影响较小。因此,工程上可根据需要适当减小分布板进气方向与水平方向的夹角来增加分布板上部颗粒浓度分布。 相似文献
8.
ZAKHARENKO A.A. 《浙江大学学报(A卷英文版)》2007,8(4):669-674
Acoustic wave propagation in piezoelectric crystals of classes?43m and 23 is studied. The crystals Tl3VS4 and Tl3TaSe4 (43m) of the Chalcogenide family and the crystal Bi12TiO20 (23) possess strong piezoelectric effect. Because the surface Bleustein-Gulyaev waves cannot exist in piezoelectric cubic crystals, it was concluded that new solutions for shear-horizontal surface acoustic waves (SH-SAWs) are found in the monocrystals using different electrical boundary conditions such as electri- cally “short” and “open” free-surfaces for the unique [101] direction of wave propagation. For the crystal Tl3TaSe4 with coefficient of electromechanical coupling (CEMC) Ke2=e2/(C×g)～1/3, the phase velocity Vph for the new SH-SAWs can be calculated with the following formula: Vph=(Va Vt)/2, where Vt is the speed of bulk SH-wave, Vt=Vt4(1 Ke2)1/2, Va=aKVt4, aK=2[Ke(1 Ke2)1/2-Ke2]1/2, and Vt4=(C44/ρ)1/2. It was found that the CEMC K2 evaluation for Tl3TaSe4 gave the value of K2=2(Vf–Vm)/Vf～0.047 (～4.7%), where Vf～848 m/s and Vm~828 m/s are the new-SAW velocities for the free and metallized surfaces, respectively. This high value of K2(Tl3TaSe4) is significantly greater than K2(Tl3VS4)～3% and about five times that of K2(Bi12TiO20). 相似文献
9.
Raymond Goulder Graham W. Scott Lisa J. Scott 《International Journal of Science Education》2013,35(8):1385-1406
It is widely held among biology teachers that fieldwork is valuable, but little is heard about students' perception of fieldwork or about the reasons for their liking or disliking fieldwork. This paper uses data from students to explore the hypotheses (1) that biology students with a positive perception of fieldwork have a less positive perception of laboratory work and vice versa and (2) that perception of fieldwork is related to demographic/personal factors and/or to pre-university perceptions and experience of fieldwork. Numeric indices of appreciation of biology field and laboratory work (I field and I lab) were determined using questionnaire information from 54 students. I field and I lab were positively correlated and there was no evidence of polarization of views; the problem that some students have a poor perception of both needs to be addressed. Mature students had a more positive view of fieldwork than 18–20-year-olds. However, regression analysis of I field against principal components suggested that demographic/personal factors had relatively little overall influence (< 20%) on appreciation of fieldwork. Perception of fieldwork at university was related to the rank given to fieldwork when choosing a university course. However, students who had participated in pre-university fieldwork did not have a more positive perception of university fieldwork; although students who recalled a worst memory of pre-university fieldwork had a less positive perception of fieldwork at university. The seeming mixed relevance of pre-university fieldwork suggests that the relationship between perception of fieldwork undertaken at university and quality of pre-university fieldwork is an area for future research. 相似文献
10.
In this paper, it is proved that the radial pth mean body RpK（p 〉 0） is homothetic to the difference body DK when K is a simplex, Furthermore, the equality Rp（Rq） = Rq（Rp） is established when p 〉 0 and q 〉 0. It is also proved the Brunn-Minkowski inequality of radial pth mean body of simplex and uniqueness property. 相似文献
11.
利用蒸发法制备了含有TiO_2的自清洁涂料,考察了相关条件对涂层材料自清洁效果的影响。结果显示:随着TiO_2含量的增加,涂层干燥时间逐渐提高,涂层的水接触角增大;TiO_2含量为15%时涂层的光催化性能最强;含TiO_2的涂层对灰尘、油污、咖啡都具有较好的自清洁效果,其机械性能满足涂料应用的一般性要求。 相似文献
12.
(K0.47Na0.47Li0.06)NbO3 (KNLN) lead-free ceramics were prepared by molten salt synthesis (MSS) method using k2CO3-Na2CO3 eutectic mixtures as the flux. The microstructure and piezoelectric properties when sintered at 980-1 030 ℃ were investigated. The calcined powders were examined by X-ray diffraction. The microstructure of the calcined powders and sintered bodies was observed using a scanning electron microscope (SEM).The piezoelectric constant d33 was measured using a quasi-static piezoelectric d33 meter. The planar coupling coefficient Kp was calculated by resonance-antiresonance method. The experimental data for each sample's performance indicators were the average values of 8 specimens. The relative densities of sintered specimens are above 97%, and the dielectric loss is below 0.03. It was found that (K0.47Na0.47Li0.06)NbO3 prepared by MSS is compact and lead-free. The piezoelectric constant d33 is 216 pC·N-1 and the planar electromechanical coupling factor Kp is 0.352. 相似文献
13.
Based on load separation theory, the load separation parameter Spb method is an effective approach for estimating the J-resistance curve from records of load versus displacement directly, using one sharp cracked specimen and an additional reference blunt cracked specimen. However, the effect of the reference blunt cracked specimen on J-resistance determination was not explicitly considered in past work. In this paper, a modified load separation parameter Spb method was developed to eliminate this effect, and then a unique estimation of instantaneous crack length for one sharp cracked specimen could be obtained. Furthermore, a forced blunting calibration method was also adopted to determine the instantaneous crack length in the load inseparable region, referring to a normalization method. Experiments on steam turbine rotator steel Cr2Ni2MoV were carried out to estimate J-resistance curves using an unloading compliance method. By removing unload and reload data from load-displacement records, the J-resistance curve for the same sharp cracked specimen was estimated using the modified separation parameter Spb method. The results indicate that the modified Spb method completely eliminates the effect of the reference blunt cracked specimen on the instantaneous crack length determination of the sharp cracked specimen. However, different J-resistance curves in a small range of crack extension are present when different blunting coefficients are used in the blunting line equation. The J-resistance curve obtained from the modified Spb method agrees well with that obtained from the compliance method. 相似文献
14.
The definition of J-integral of interfacial crack was introduced. The three-point bending tests were carried out to obtain the critical loading
values when the interfacial crack initiation occurred between coatings and substrates. The finite element analysis (FEA) was
adopted to analyze the stress distribution in the specimens and compute the J-integral of the interfacial crack between LX88A coating and Chinese Q345 steel. The results showed that the average value
of critical J-integral is 0.70 N/m, which can be taken as the fracture parameter to evaluate the interfacial fracture behavior for the
three-point bending specimens of LX88A coating/Q345 steel system.
Supported by Tianjin Natural Science Foundation (No.08JCYBJC09100), New Teacher Research Fund for the Doctoral Program of
Higher Education of China (No.20070056096) and New Century Outstanding Talented Person Plan of China.
XU Lianyong, born in 1975, male, Dr. 相似文献
15.
In this note, we prove that the convergence rate of the modified Gauss-Seidel (MGS) method with preconditional I Sa isa monotonic function of preconditioning parameter a. Based on this result, to achieve better convergence rate we suggest proformingtwice preconditoning when applying the MGS method to solve a linear system whose coefficient matrix is an irreducible non-singularM-matrix. 相似文献
16.
Consider the positive d-dimensional lattice d (d≥2) with partial ordering ≤, let {XK; K ∈ d } be i.i.d. random vari- ables taking values in a real separable Hilbert space (H, ||·||) with mean zero and covariance operator ∑, and set partial sums SN =∑K≤NXK, K , N ∈ d . Under some moment conditions, we obtain the precise asymptotics of a kind of weighted infinite series for partial sums SN as ε 0 by using the truncation and approximation methods. The results are related to the convergence rates of the law of the logarithm in Hilbert space, and they also extend the results of (Gut and Spǎtaru, 2003). 相似文献
17.
This study of the thermal decomposition kinetics of various average diameter nano-particles of calcium carbonate by means
of TG-DTA (thermogravimetry and differential thermal analysis) showed that the thermal decomposition kinetic mechanisms of
the same crystal type of calcium carbonate samples do not vary with decreasing of their average diameters; their pseudo-active
energyE
a; and that the top-temperature of decompositionT
p decreases gently in the scope of micron-sized diameter, but decreases sharply when the average diameter decreases from micron
region to nanometer region. The extraordinary properties of nano-particles were explored by comparing the varying regularity
of the mechanisms and kinetic parameters of the solid-phase reactions as well as their structural characterization with the
variation of average diameters of particles. These show that the aggregation, surface effect as well as internal aberrance
and stress of the nano-particles are the main reason causing bothE
a andT
p to decline sharply with the decrease of the average diameter of nano-particles.
Project supported by Guizhou Province Natural Science Foundation of China 相似文献
18.
WANG Ya-qin 《浙江大学学报(A卷英文版)》2007,8(10):1691-1694
Let K be a closed convex subset of a real reflexive Banach space E, T：K→K be a nonexpansive mapping, and f：K→K be a fixed weakly contractive （may not be contractive） mapping. Then for any t∈（0, 1）, let x1∈K be the unique fixed point of the weak contraction x1→tf（x）＋（1-t）Tx. If T has a fixed point and E admits a weakly sequentially continuous duality mapping from E to E^＊, then it is shown that {xt} converges to a fixed point of T as t→0. The results presented here improve and generalize the corresponding results in （Xu, 2004）. 相似文献
19.
Silicon carbide (SiC) composites were prepared by hot-press sintering from α-SiC starting powders with BaAl2Si2O8 (BAS). The effects of additives on densification, microstructure, flexural strength, and fracture behavior of the liquid phase sintered (LPS) SiC composites were investigated. The results show that the served BAS effectively promotes the densification of SiC composites. The flexural strength and fracture toughness of the SiC composites can reach a maximum value of 454 MPa and 5.1 MPa·m1/2, respectively, for 40% (w/w) BAS/SiC composites. SiC grain pullout, crack deflection, and crack bridging were main toughening mechanisms for the sintered composites. 相似文献
20.
基于Paris 公式建立TBM 刀盘的裂纹扩展模型,利用Workbench 模拟裂纹的开裂过程,计算出其循环次数与应力强度因子。 并改变双裂纹的初始长度、距离、角度,分析多部位损伤时筋板的裂纹扩展寿命。 结果表明,裂纹的初始长度越长构件越容易失效,每增加2.5 mm 寿命将减少35%,而双裂纹距离对寿命的影响较小,在10%以内。 当裂纹方向和受力方向垂直时,构件容易失效,反之则对寿命的影响越小。 该研究可为刀盘设计过程中疲劳寿命领域提供参考。 相似文献