Effects of a Time-Varying Test Environment on the Evaluation of Dynamic Stability with Application to Flutter Testing

An approach for dynamic stability analysis of a cracked rotor system with transverse crack is addressed here. The time-varying area moments of inertia of the cracked section are employed in formulating the time-periodic finite element stiffness matrix which yields a linear time-periodic system. The harmonic balance method (HB) is used in solving the finite element (FE) equations of motion for studying the dynamic stability of the system. The sign of the determinant of the scaled coefficient matrix resulting from applying the HB solution to the cracked rotor system is found to be a reliable approach for identifying the major unstable regions of the system in the parameter plane obtained by plotting the shaft speeds of rotation vs. the crack depths. Specifically, the negative values of the determinant of this scaled coefficient matrix identify the unstable regions of the cracked system. This approach is applied here to the parametrically excited Mathieu’s equation, two degree-of-freedom gyroscopic system, and then to the FE model of the cracked rotor system. The results of applying this approach are verified using the Floquet’s theory. Compared with the theory, the sign of the determinant of the scaled coefficient matrix is found here to be an efficient tool for identifying the unstable regions of linear parametrically excited systems, especially the large scale dynamic systems where this approach requires considerably less computational time than the Floquet’s theory.

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Correlation between dislocation, grain boundary and interface of duplex SS in stress corrosion cracking(SCC)

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100177775 ◽

1990 ◽

Vol 48 (4) ◽

pp. 928-929

Author(s):

Wang Zheng-fang ◽

Z.F. Wang

Keyword(s):

Stainless Steel ◽

Thermal Cycle ◽

Secondary Phase ◽

Corrosion Cracking ◽

Coarse Grained ◽

Test Environment ◽

Fine Grained ◽

Evaluation Test ◽

Welding Thermal Cycle ◽

Micro Analysis

The main purpose of this study highlights on the evaluation of chloride SCC resistance of the material,duplex stainless steel,OOCr18Ni5Mo3Si2 (18-5Mo) and its welded coarse grained zone(CGZ).18-5Mo is a dual phases (A+F) stainless steel with yield strength:512N/mm2 .The proportion of secondary Phase(A phase) accounts for 30-35% of the total with fine grained and homogeneously distributed A and F phases(Fig.1).After being welded by a specific welding thermal cycle to the material,i.e. Tmax=1350°C and t8/5=20s,microstructure may change from fine grained morphology to coarse grained morphology and from homogeneously distributed of A phase to a concentration of A phase(Fig.2).Meanwhile,the proportion of A phase reduced from 35% to 5-10°o.For this reason it is known as welded coarse grained zone(CGZ).In association with difference of microstructure between base metal and welded CGZ,so chloride SCC resistance also differ from each other.Test procedures:Constant load tensile test(CLTT) were performed for recording Esce-t curve by which corrosion cracking growth can be described, tf,fractured time,can also be recorded by the test which is taken as a electrochemical behavior and mechanical property for SCC resistance evaluation. Test environment:143°C boiling 42%MgCl2 solution is used.Besides, micro analysis were conducted with light microscopy(LM),SEM,TEM,and Auger energy spectrum(AES) so as to reveal the correlation between the data generated by the CLTT results and micro analysis.

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Molecular insights on the dynamic stability of peptide nucleic acid functionalized carbon and boron nitride nanotubes

Physical Chemistry Chemical Physics ◽

10.1039/d0cp05759b ◽

2021 ◽

Vol 23 (1) ◽

pp. 219-228

Author(s):

Nabanita Saikia ◽

Mohamed Taha ◽

Ravindra Pandey

Keyword(s):

Nucleic Acid ◽

Boron Nitride ◽

Nucleic Acids ◽

Dynamic Stability ◽

Peptide Nucleic Acid ◽

Rational Design ◽

Peptide Nucleic Acids ◽

Boron Nitride Nanotubes ◽

Molecular Hybrids ◽

Single Wall Nanotubes

The rational design of self-assembled nanobio-molecular hybrids of peptide nucleic acids with single-wall nanotubes rely on understanding how biomolecules recognize and mediate intermolecular interactions with the nanomaterial's surface.

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Manipulate Me

European Journal of Psychological Assessment ◽

10.1027/1015-5759/a000534 ◽

2020 ◽

Vol 36 (4) ◽

pp. 554-562

Author(s):

Alica Thissen ◽

Frank M. Spinath ◽

Nicolas Becker

Keyword(s):

High School Students ◽

Spatial Ability ◽

Convergent Validity ◽

Item Difficulty ◽

Test Results ◽

Response Elimination ◽

School Students ◽

Test Environment ◽

Response Options ◽

Construction Task

Abstract. The cube construction task represents a novel format in the assessment of spatial ability through mental cube rotation tasks. Instead of selecting the correct answer from several response options, respondents construct their own response in a computerized test environment, leading to a higher demand for spatial ability. In the present study with a sample of 146 German high-school students, we tested an approach to manipulate the item difficulties in order to create items with a greater difficulty range. Furthermore, we compared the cube task in a distractor-free and a distractor-based version while the item stems were held identical. The average item difficulty of the distractor-free format was significantly higher than in the distractor-based format ( M = 0.27 vs. M = 0.46) and the distractor-free format showed a broader range of item difficulties (.02 ≤ pi ≤ .95 vs. .37 ≤ pi ≤ .63). The analyses of the test results also showed that the distractor-free format had a significantly higher correlation with a broad intelligence test ( r = .57 vs. r = .17). Reasons for the higher convergent validity of the distractor-free format (prevention of response elimination strategies and the broader range of item difficulties) and further research possibilities are discussed.

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