Stress around the hole of single lapped and single bolted joint plates with fitting clearance

Wenguang Liu,Weiyan Lin 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.4

The effects of parameters on the stress distribution around the plate hole of a bolted joint having clearance fitting were investigated in this work. The main purpose is to reveal the interaction mechanism of different parameters and stress around a hole by theory and simulation analysis. Primarily, elastic theory was employed to derive the equilibrium equation of stress of the bolted joint plate. Subsequently, the effects of parameters, such as the bolt-hole clearance, the degree of bolt misalignment, and the pre-tightening force, on the stress around the plate hole of a bolted joint were analyzed qualitatively. Thereafter, a parametric model of single-lapped and single-bolted joint plate was created and analyzed through ABAQUS and a Python program. Finally, the effects of bolt-hole clearance, bolt misalignment, and pre-tightening force on the stress distribution around the hole were examined by case studies. Results corroborates that these parameters influence the stress magnitude around the hole and that the stress magnitude varies nonlinearly with the change in parameters. This work provides a good reference for the dynamic design of bolted joint plates.

Frequency error based identification of cracks in beam-like structures

Wenguang Liu,Mark E. Barkey 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.10

A crack identification method of a single edge cracked beam-like structure by the use of a frequency error function is presented in this paper. First, the dynamic theory of Euler-Bernoulli beams was employed to derive the equation of the natural frequency for a single edge cracked cantilever beam-like structure. Subsequently, the cracked section of the beam was simulated by a torsional spring. The flexibility model of the torsional spring due to the crack was estimated by fracture mechanics and energy theory. Thereafter, a function model was proposed for crack identification by using the error between the measured natural frequencies and the predicted natural frequencies. In this manner, the crack depth and crack position can be determined when the total error reaches a minimum value. Finally, the accuracy of the natural frequency equation and the viabilty of the crack identification method were verified in the case studies by the measured natural frequencies from the literature. Results indicate that the first two predicted natural frequencies are in good agreement with the measured ones. However, the third predicted natural frequency is smaller than the measured natural frequency. In the case of small measured frequency errors, the predicted crack parameters are in good agreement with the measured crack parameters. However, in the case of large measured frequency errors, the predicted crack parameters only give roughly estimated results.

Nonlinear vibrational response of a single edge cracked beam

Wenguang Liu,Mark E. Barkey 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.11

The nonlinear vibrational response of a breathing cracked beam was investigated. The study was done by using a new crack stiffness model to examine some of the nonlinear behaviors of a cantilever beam with a breathing crack. The quadratic polynomial stiffness equation of the cracked beam was derived based on the hypothesis that the breathing process of a crack depends on the vibration magnitude. The Galerkin method combined with the stiffness equation was used to simplify the cracked beam into a Single-degree-of-freedom (SDOF) lumped system with nonlinear terms. The multi scale method was adopted to analyze the nonlinear amplitude frequency response of the beam. The applicability of the stiffness model was discussed and parameter sensitivity studies on the dynamic response were carried out by the SDOF model for a cantilever beam. Results indicate that the new stiffness model provides an efficient tool to study the vibrational nonlinearities introuduced by the breathing crack. Therefore, it might be used to develop a nonlinear identification method of a crack in a beam.

Analysis of the modal frequency of a functionally graded cylindrical shell

Chao Liu,Wenguang Liu 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.3

The modal frequencies of a functionally graded material (FGM) cylindrical shell with different geometry dimensions and material constituents are studied under eight boundary conditions. The main goal is to reveal the influencing mechanism of different factors on the modal frequencies of the FGM shell. Firstly, the Voigt model is used to describe the properties of FGM. Secondly, the motion equation of the FGM shell is derived using Hamilton’s principle. Thirdly, the modal frequency equation of the FGM shell is obtained based on a trigonometric function for the eight boundary conditions. Lastly, the effects of geometry dimension, material constituents, and boundary conditions on the modal frequencies of the FGM shell are analyzed through case studies. Results indicate that the modal frequencies obtained are good agreement with those from previous literature and the finite element method. The geometry dimensions of the FGM shell, the material constituents of the FGM, and the boundary conditions are crucial to the modal frequencies. This work can serve as a reference for the design of FGM and optimization of the structure of FGM shells.

Analysis of nonlinear vibration response of a functionally graded truncated conical shell with piezoelectric layers

Yuhang Zhang,Wenguang Liu,Zhipeng Lyu,Chao Liu,Lei Pang 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.8

The nonlinear vibration response of a functionally graded materials (FGMs) truncated conical shell with piezoelectric layers is analyzed. The vibration amplitude is suppressed by the positive and inverse piezoelectric effects. And the bifurcation phenomenon is described to reveal the motion state of the conical shell. Firstly, a truncated conical shell composed of three layers is described. And the effective material properties of the FG layer are defined by the Voigt model and the power law distribution. Next, the electric potentials of piezoelectric layers are defined as cosine distribution along the thickness direction. Meanwhile, the constant gain negative velocity feedback algorithm is used to suppress the vibration amplitude by the electric potential produced by the sensor layer. Thereafter, considering the first-order shear deformation theory and the von Karman nonlinearity, the relationship between the strain and displacement is defined. And the corresponding energy of the conical shell is calculated. After that, the motion equations of the conical shell are derived based on the Hamilton principle. Again, the nonlinear single degree of freedom equation is derived by the Galerkin method and the static condensation method. In the end, the nonlinear vibration response of FGMs truncated conical shell with piezoelectric layers under the external excitation is analyzed via using the harmonic balance method and the Runge-Kutta method. The effects of various parameters, such as ceramic volume fraction exponent, external excitation’s amplitude, control gain and geometric parameters on the nonlinear vibration response of the system are evaluated by case studies. Results indicate that the control gain plays an important role on the suppression of the vibration amplitude. The ceramic volume fraction exponents are not sensitive to the nonlinear vibration response compared with other parameters. The bifurcation behavior is observed under different parameters. The FGMs truncated conical shell with piezoelectric layers has three types of motion state, such as periodic motion, multi-periodic motion, and chaos motion.

Thermo-electro-mechanical vibration and buckling analysis of a functionally graded piezoelectric porous cylindrical microshell

Zhipeng Lyu,Wenguang Liu,Chao Liu,Yuhang Zhang,Mengxiang Fang 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.10

In this paper, the vibration and buckling behavior of a functionally graded piezoelectric porous cylindrical microshell under thermo-electro-mechanical loads are explored on the basis of modified couple stress theory and higher-order shear deformation theory. First, the model of a functionally graded piezoelectric porous cylindrical microshell composed of piezoelectric materials with gradient change in the thickness direction was described. Second, the governing equations of the microshell were derived by Hamilton's principle and Maxwell equation. Third, the modal frequency and buckling equations of the microshell with simply supported ends were obtained on the basis of harmonic trigonometric functions. Finally, the effects of parameters on the modal frequency and buckling behavior were carried out by case studies. The results show that the modal frequency of the microshell can be adjusted by changing the porosity volume fraction, power index, applied voltage, axial load and geometric dimensions. It is also found that the vibration of the microshell is suppressed by positive voltage and axial compression but is strengthened by negative voltage and axial tension, and the material length scale parameter increases stiffness. In addition, the effects of applied voltage and axial load on the buckling behavior are larger than those of temperature. Results can be used to guide the design and application of piezoelectric devices.

Genetic variation of Vp1 in Sichuan wheat accessions and its association with pre-harvest sprouting response

Jirui Wang,Yaxi Liu,Yan Wang,Zhenhong Chen,Shuai Dai,Wenguang Cao,George Fedak,Xiujing Lan,Yuming Wei,Dengcai Liu,Youliang Zheng 한국유전학회 2011 Genes & Genomics Vol.33 No.2

Pre-harvest sprouting (PHS) in bread wheat is a major abiotic constraint reducing yield and influencing the production of high quality grain. In China both spring and winter wheat regions are affected by PHS. Sichuan lies in southwest China,where the most of rainfall occurs during April to September when wheat is harvested. The present investigation was conducted to identify the allelic variability of Vp1, a gene that plays a role in maintenance and induction of dormancy,among Sichuan landraces and recent cultivars with different dormancy levels and to find potential sources of PHS resistance for breeding. Sichuan landrace and cultivar wheat accessions had a wide range of dormancy levels. The average germination index (GI) of Sichuan landrace accessions was 0.232, whereas at 0.674 it was much higher for cultivars. The different dormancy levels between landraces and cultivars indicated that pre-harvest sprouting resistance might have been neglected in recent Sichuan wheat breeding programs. The average GI of white grained accessions was higher than for red grained accessions. Particular Vp-1B gene fragments were specific in landraces or cultivars and in white or red grained accessions. The results indicated that Vp-1B markers could be used to distinguish cultivars and landraces. Significant relationships between certain Vp-1B allelesand GI of Sichuan wheat accessions were shown by Spearman’s rank correlation analysis.

Experimental and numerical studies of miniature bar-typed structural fuses with Teflon pads

Sen Yang,Yan Liu,Yu Lin,Dongzhi Guan,Hanbin Ge,Zhengxing Guo,Wenguang Liu 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.41 No.4

Many studies have proved that structural fuses could improve the seismic performance of structures efficiently. A structural fuse named the miniature bar-typed structural fuse (MBSF) has been proposed and investigated by the authors, which consists of a central core bar, a confining tube. To further improve the mechanic performances of the MBSFs under compressive loadings, Teflon pads are introduced to adjust the contact and friction status between the core bar and the confining tube. Three groups of specimens were discussed including the specimen with a single cutting line (SC), the specimen with double cutting lines (DC), and the specimen with triple cutting lines (TC). The results show that the hysteretic performances of the fuses are improved with the help of Teflon pads. The compression strength adjustment factor declines when Teflon pads are appended. Numerical and theoretical analyses are also conducted which expounded the effect of the Teflon pads. Different plastic buckling deformation principles of the core bars are compared by the theoretical analysis. It is shown that Shanley’s theory fits the numerical results well, which is recommended for the theoretical calculation of the proposed MBSFs.

A new thermosensitive polymer as nonadhesive liquidembolism material

Chengru Zhao,Qin Wang,Jianwen Meng,Wenguang Liu,Zuoqin Liu 한국물리학회 2005 Current Applied Physics Vol.5 No.5

Thermosensitive copolymers poly(NIPAm-co-NNPAm) ofN-isopropylacrylamide (NIPAm) withN-n-propylacrylamide(NNPAm) were synthesized by free radical copolymerization using potassium persulfate (KPS) and sodium sulte (Na2SO3) as ini-tiator. FTIR and1H NMR conrmed the structure of the copolymer poly(NIPAm-co-NNPAm). The dynamic mechanical analysisand dynamic contact angle were determined. The lower critical solution temperature (LCST) of copolymers was investigated byDSC. The results indicated the LCST decreased with the higher NNPAm contents. The phase transition of the copolymer solutionoccurred at body temperature within 30 s and the copolymers changed into soft solids. The copolymer could be used as a new non-adhesive liquid embolism material for the intervenient therapy of the cerebral arterio-venous malformation (AVM)..

Variations in mitochondrial cytochrome b region among Ethiopian indigenous cattle populations assert Bos taurus maternal origin and historical dynamics

Tarekegn, Getinet Mekuriaw,Ji, Xiao-yang,Bai, Xue,Liu, Bin,Zhang, Wenguang,Birungi, Josephine,Djikeng, Appolinaire,Tesfaye, Kassahun Asian Australasian Association of Animal Productio 2018 Animal Bioscience Vol.31 No.9

Objective: This study was carried out to assess the haplotype diversity and population dynamics in cattle populations of Ethiopia. Methods: We sequenced the complete mitochondrial cytochrome b gene of 76 animals from five indigenous and one Holstein Friesian${\times}$Barka cross bred cattle populations. Results: In the sequence analysis, 18 haplotypes were generated from 18 segregating sites and the average haplotype and nucleotide diversities were $0.7540{\pm}0.043$ and $0.0010{\pm}0.000$, respectively. The population differentiation analysis shows a weak population structure (4.55%) among the populations studied. Majority of the variation (95.45%) is observed by within populations. The overall average pair-wise distance ($F_{ST}$) was 0.049539 with the highest ($F_{ST}=0.1245$) and the lowest ($F_{ST}=0.011$) $F_{ST}$ distances observed between Boran and Abigar, and Sheko and Abigar from the indigenous cattle, respectively. The phylogenetic network analysis revealed that all the haplotypes detected clustered together with the Bos taurus cattle and converged to a haplogroup. No haplotype in Ethiopian cattle was observed clustered with the reference Bos indicus group. The mismatch distribution analysis indicates a single population expansion event among the cattle populations. Conclusion: Overall, high haplotype variability was observed among Ethiopian cattle populations and they share a common ancestor with Bos taurus.