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1.
1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　Ｔｈｅｓｔｒｅｓｓｉｎｔｅｎｓｉｔｙｆａｃｔｏｒ(ＳＩＦ)ｏｆｔｈｅｓｅｍｉｅｌｌｉｐｔｉｃａｌｓｕｒｆａｃｅｃｒａｃｋｎｅｅｄｓｔｏｂｅｃａｌｃｕｌａｔｅｄｆｏｒｅｖａｌｕａｔｉｎｇｔｈｅｓｔｒｅｎｇｔｈｏｆｍｅｔａｌｃｏｍｐｏｎｅｎｔｓｂｅｃａｕｓｅｍａｎｙｆｌａｗｓｏｃｃｕｒｏｎｔｈｅｃｏｍｐｏｎｅｎｔｓｕｒｆａｃｅｄｕｅｔｏｔｈｅｎａｎｕｆａｃｔｕｒｅａｎｄｔｒａｎｓｐｏｒｔｐｒｏｃｅｄｕｒｅ.Ｕｐｔｏｎｏｗ,ｓｏｌｖｉｎｇｔｈｒｅｅｄｉｍｅｎｓｉｏｎａｌｃｒａ…  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.
Hydroxyapatite bioceramics is simulated by using finite element method (FEM).The influences of porosity,hole shape,angle of crack and other parameters on the ceramics are analyzed.The results show that with the increase of the angle between crack and horizontal direction,the stress intensity factor KⅠdecreases gradually,but stress intensity factor K II increases at first and then it decreases.The value of K Ⅱ reaches maximum when the angle between crack and horizontal direction is 45°.KⅠ and K Ⅱ rise with the increase of porosity,and they are almost the same for the circular and hexagonal holes.For elliptical holes,KⅠand KⅡreach maximum when the long axis of ellipse is perpendicular to the loading direction and they reach minimum when the same axis is parallel to the loading direction.Moreover,with the increase of the angle between the long axis and loading direction,KⅠ and KⅡ increase gradually.  相似文献   

4.
The achievement motive concept refers to a relatively stable personality characteristic in terms of a capacity to anticipate affects in achievement situations. The motive to achieve success (M s ) refers to the individual's capacity to anticipate positive affects, and the motive to avoid failure (M f ) refers to a capacity to anticipate negative affects in achievement situations. Based, among other things, on the conceptualizations of motives, a measurement was constructed to tap the two aspects (M s and M f ) of motivation. Over the years the scale has been translated to several languages and used in a number of studies. The Czech version of the scale is an adapted translation of the English one, and was administered to 179 pupils in the sixth grade in 1989. Further, the subjects were retested after an interval of 12 weeks. The analyses indicate that the psychometric properties of the Czech version of AMS are promising.  相似文献   

5.
Congruences for finite triple harmonic sums   总被引：1，自引：0，他引：1  
Zhao (2003a) first established a congruence for any odd prime p>3, S(1,1,1;p)≡-2Bp-3 (mod p), which holds when p=3 evidently. In this paper, we consider finite triple harmonic sum S(α,β,γ;p) (mod p) is considered for all positive integers α,β,γ. We refer to w=α β γ as the weight of the sum, and show that if w is even, S(α,β,γ;p)≡0 (mod p) for p≥w 3; if w is odd, S(α,β,γ;p)≡rBp≥w (mod p) for p≥w, here r is an explicit rational number independent of p. A congruence of Catalan number is obtained as a special case.  相似文献   

6.
Pascual‐Leone (1972) has conducted task analyses in terms of M‐demand (amount of information processing required by the task) and demonstrated that the phenomenon of ‘horizontal decalages’, described by Piaget, can be accounted for by increasing demands of information processing. It has been shown that formal operational reasoning is required to balance even simple, one‐step chemical equations, while formal reasoning and a sufficiently large M‐capacity are required to balance more complex, multi‐step chemical equations. The objective of the present study is to investigate the relation between functional M‐capacity (Mf) and student performance in solving chemistry problems of increasing M‐demand. It was found that student performance decreased as the M‐demand of the problems increased. Similarly, the correlation coefficients between Mf‐ and student performance increased progressively as the M‐demand of the problems increased.  相似文献   

7.
In this paper, a semi on-line version on m identical machines M1 , M2, …, Mm ( m ≥ 3 ) was considered, where the processing time of the largest job is known in advance. Our goal is to maximize the minimum machine load, an NPLS algorithm was presented and its worst-case ratio was proved to be equal to m - 1 which is the best possible value. It is concluded that if the total processing time of jobs is also known to be greater than (2 m - 1 )Pmax where pmax is the largest job‘s processing time, then the worstcase ratio is 2 - 1/m.  相似文献   

8.
The properties of a two-dimensional vortex system with random columnar defects were studied by cooling the vortex system to zero temperature. The vortex lattice became more and more disordered with increasing pinning strengthf p. At smallf p, a triangular vortex, lattice away from the pins was observed. The peak of structure factorS(G0) of the vortex lattice decreased with pinning strengthf p, which accorded with the finding that the probability of vortex to be pinned increased withf p. Some of our results agreed with experimental findings. Project supported by the Ministry of Science and Technology of China (NKBRSF-G19990646) and Zhejiang Province Scientific Foundation (199031).  相似文献   

9.
Most Piagetian formal operational reasoning tasks show horizontal decalage; that is, subjects pass certain tasks and fail others that have the same logical structure. The study reported here analyzes the importance of individual difference variables, as postulated by the neo-Piagetian theory of Pascual-Leone, in explaining subject performance in formal reasoning. A sample of 72 freshman students were administered a test of formal reasoning having 20 items of different types of reasoning, and the tests of the individual difference variables. Results obtained from multiple regression analyses show that Pascual-Leone's structural M-capacity (Ms) is the most consistent predictor of success in the different formal reasoning tasks, followed by Witkin's cognitive style, and to a much lesser degree Raven's progressive matrices, and Pascual-Leone's functional M-capacity (Mf). It was found that in the total score on the 20 items of formal reasoning, Ms accounted for 23.3% of the variance (R = 0.483, F = 6.39, p = 0.014) and Witkin's Group Embedded Figures Test, increased the multiple R significantly (F = 7.77, p = 0.007) and accounted for 7.6% of the variance. Mf and the Raven test did not make a significant contribution to the regression equation. Correlation coefficients among most of the items having the same reasoning pattern but different content are generally low but statistically significant (p < 0.01). Intercorrelations among items having the same formal reasoning pattern and content are fairly high (p < 0.001). These results emphasize the importance of individual difference variables: information-processing capacity (Pascual-Leone) and oversensitivity to potentially misleading information (Witkin). It is suggested that in order to understand student performance in formal reasoning tasks, we should expect horizontal decalages as a rule and not the exception, as Piaget had postulated. Educational implications are drawn.  相似文献   

10.
Novel ZTA/Al2O3-SiCw-TiC polyphase ceramics were fabricated by hot pressing techniques. Phase transformation toughening, particle dispersion and whisker reinforcement have obviously superposed strengthening and toughening effects. It is observed that ZTA-20SiCw-20TiC has better comprehensive mechanical properties compared with Al2O3-20SiCw-20TiC. For the optimum processing, the ZTA-20SiCw-20TiC exhibited a flexural strength of 567MPa, a fracture toughness of 6.3MPa·m0.5, a hardness of HRA93.6 and a relative density of ≥99.6 %. The tensile stress in matrix introduced by SiC whisker and TiC could be relaxed by the compress stress produced by tetragonal zirconia (ZrO2(t)) transformation. TiC formed a continuous skeleton which prevented the grain growth of the matrix. The grain sizes of the matrix became finer with increasing TiC. The major fracture mode of the matrix was transcrystalline cleavage rupture. Supported by the Young Science Foundation of Shanghai Municipal Commission of Education(98QN55)  相似文献   

11.
The copolymerization of CO and styrene catalyzed by Pd/C toward the formation of polyketones(PK)was studied in the N-valeronitrile-N'-methylimidazolium hexafluorophosphate([C4CNmim]+PF-6) medium. The synthesized PK was characterized by Fourier transform infrared(FTIR), elemental analysis, 13C-nuclear magnetic resonance(13C-NMR), differential scanning calorimetry(DSC), thermogravimetric analysis(TGA) and gel permeation chromatography(GPC). The supported ionic liquid film on the surface of Pd/C catalyst can prevent the products from covering the hole of active carbon due to its chemical stability and weak coordination ability with metal ions, and thus efficiently improve the catalytic activity. The effects of different amounts of ionic liquid on the catalytic activity and reusability of the catalyst and the molecular weight of PK were discussed. When the usage of ionic liquid is 10wt%(0.1 g ionic liquid / 1 g active carbon carrier) and the theoretical content of Pd2+ is 5wt%(0.05 g Pd2+/ 1 g active carbon carrier), the highest catalytic activity 2 963.64 gSTCO/(gPd·h) is achieved with the molecular weight and polydispersity index of PK as Mn=9 684, Mw=13 452 and Mw /Mn=1.389.  相似文献   

12.
Out-of-plane angular dependence of ferromagnetic resonance spectra was measured in sputtered Co/Pt multilayers and analyzed with the Landau-Lifshitz-Gilbert equation. The effective demagnetizing field 4πMeff is found to increase with decreasing tPt and decreasing 1/tco, which can be considered as a result of interplay between the interlayer coupling and a lowdimensional effect. The g factor increases with increasing tpt and decreasing tCo, indicating contribution of spin-polarization of Pt atoms and additional contribution of orbital moment of Co atoms. The in-plane resonance line-width increases with decreasing too and increases with increasing tPt.  相似文献   

13.
The aim of this research is to characterize the development of fatigue damage by means of stress-strain hysteresis. Experiments were conducted on 14 specimens made of cold-finished unannealed AISI 1018 steel. Results demonstrate that the mechanical hysteresis loop areas, when plotted as a function of the number of loading cycles, show significant variations and demonstrate the three principal stages concerning the progress of the fatigue failure--initial accommodation, accretion of damage and terminal failure. These three stages of fatigue are marked by the transitions at cycles N2 and N3. Experimental results show that although fatigue life Nf ranges from 2644 cycles to 108 992 cycles, the ratios of N2/Nf and N3/Nf tend to be stable： N2/Nf=I 0.7%, N3/Nf=91.3%.  相似文献   

14.
１ＩｎｔｒｏｄｕｃｔｉｏｎＤｉｆｅｒｅｎｔｉａｌｅｑｕａｔｉｏｎｓｗｉｔｈｔｕｒｎｉｎｇｐｏｉｎｔｓｅｘｉｓｔｗｉｄｅｌｙｉｎｍａｎｙｐｒｏｂｌｅｍｓｏｆｍａｔｈｅｍａｔｉｃｓｐｈｙｓｉｃｓ,ｓｏｔｈｅｓｅｐｒｏｂｌｅｍｓａｒｅｖｅｒｙｉｍｐｏｒｔａ...  相似文献   

15.
Guided by the Theory of Racial Socialization in Action (TRSA; Smith-Bynum in press), this study examined observed caregiver-provided ethnic-racial socialization in response to a school-based discriminatory dilemma. Forty-five Black and 36 Latinx caregivers (88% mothers) with low-income and their children (Mage = 11.09, SD = 0.29; 46.3% female) participated in Dallas, Texas from 2018 to 2019. Dyads responded to a hypothetical scenario in which a school counselor makes a discriminatory comment to the child. Results of a factor mixture analysis suggested that caregivers engaged in the dialogue using one of four approaches: Low-engaged, Legacy, Racial Literacy, or High-engaged. Profiles were found to differ significantly by the race/ethnicity and language of caregivers and were associated with youth’s concurrent behavioral engagement (R2 = .04).  相似文献   

16.
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17.
The stress intensity factor (SIF) is a critical parameter associated with the fracture behaviour of materials. In this paper, we select the displacement function around a crack tip as the shape function of the digital image correlation (DIC), which makes it possible to directly calculate the SIF by the correlation scheme. Moreover, we use a non-rectangular subset, which can reduce the influence of plastic deformation and crack width on the DIC measurement accuracy. We measured the SIF of a mode I crack in a super-hard aluminium alloy specimen to verify the performance of the proposed method. Our experimental results show that a DIC with a specific shape function can be used to accurately and efficiently calculate the SIF. Furthermore, we also present a practical application of our proposed method for determining the SIF, crack propagation angle and crack tip displacement.  相似文献   

18.
Fatigue crack growth rate test using a frequency sweep method   总被引：1，自引：0，他引：1  
Fatigue crack propagation characteristics of a diesel engine crankshaft are studied by measuring the fatigue crack growth rate using a frequency sweep method on a resonant fatigue test rig. Based on the phenomenon that the system frequency will change when the crack becomes large, this method can be directly applied to a complex component or structure. Finite element analyses （FEAs） are performed to calibrate the relation between the frequency change and the crack size, and to obtain the natural frequency of the test rig and the stress intensity factor （SIF） of growing cracks. The crack growth rate i.e. da/dN-AK of each crack size is obtained by combining the testing-time monitored data and FEA results. The results show that the crack growth rate of engine crankshaft, which is a component with complex geometry and special surface treatment, is quite different from that of a pure material. There is an apparent turning point in the Paris＇s crack partition. The cause of the fatigue crack growth is also discussed.  相似文献   

19.
Given a function f and an initial value a 1, we consider properties and representations of the iteration sequence a 1 , f(a 1 ), f(f(a 1 )),.... Because iteration sequences often cannot be expressed in explicit algebraic terms, there is an emphasis on using various graphical and numerical representations. An empirical investigation examined the influence of representations on the discovery of properties and on problem solving abilities for iteration sequences. A total of 79 students (11th graders) and 22 secondary mathematics teachers participated. The empirical study was implemented with a computer program, developed by the author.  相似文献   

20.
This work investigated the microwave dielectric properties of A-site substitution by rare earth La3+in(Pb0.5Ca0.5)(Fe0.5Ta0.5)O3(PCFT) system.A single perovskite phase was obtained only when the doping content was 2%.Suitable La3+ doping improved microwave dielectric performances.Excessive La3+doping caused the formation of secondary phase,which resulted in the decreasing of permittivity εrand quality factor Qfvalues.Especially,when the doping content is 2%-5%,permittivity εrwas above 75 and Qfvalues were 6...  相似文献   

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