Dynamic analysis of auger driller during luffing motion by bond graph

To investigate the inherent complex dynamic characteristics of luffing mechanism of auger driller, the rigid body motion of structures and the dynamic behavior of the drive system should be studied in an integrated model. The working principle and structural characteristics of the luffing mechanism is firstly analyzed, then the bond graph model of revolute joint, cylinder and boom are proposed based multi-body theory, and the bond graph model of hydraulic system is also constructed. Through the analysis of the dynamic characteristics and interaction rules of each sub model, the transmission path of power flow is described. Coupling the boom structure and hydraulic actuator, the complete bond graph model of luffing mechafnism have been developed in a unified way. The total governing equations of the system have been derived from the model. Numerical results of chamber pressure of luffing cylinder implies to the good accuracy of the bond graph study, while comparing with experimental results. Meanwhile, the effects of the installation position parameters of the joints on system response have been studied through simulation, which provides a theoretical basis for improving the dynamic performance of the luffing mechanism

圧延用複合ロールの熱処理における残留応力に関する研究

九州工業大学博士学位論文（要旨）学位記番号：工博甲第433号 学位授与年月日：平成29年3月24

A Review of SMA-Based Actuators for Bidirectional Rotational Motion: Application to Origami Robots

Shape memory alloys (SMAs) are a group of metallic alloys capable of sustaining large inelastic strains that can be recovered when subjected to a specific process between two distinct phases. Regarding their unique and outstanding properties, SMAs have drawn considerable attention in various domains and recently became appropriate candidates for origami robots, that require bi-directional rotational motion actuation with limited operational space. However, longitudinal motion-driven actuators are frequently investigated and commonly mentioned, whereas studies in SMA-based rotational motion actuation is still very limited in the literature. This work provides a review of different research efforts related to SMA-based actuators for bi-directional rotational motion (BRM), thus provides a survey and classification of current approaches and design tools that can be applied to origami robots in order to achieve shape-changing. For this purpose, analytical tools for description of actuator behaviour are presented, followed by characterisation and performance prediction. Afterward, the actuators’ design methods, sensing, and controlling strategies are discussed. Finally, open challenges are discussed

Usefulness of Non-Uniform Heating and Quenching Method for Residual Stress of Bimetallic Roll: FEM Simulation Considering Creep Behavior

Bimetallic rolls are widely used in steel rolling industries because of the excellent hardness, wear resistance and high temperature properties. Controlling the residual stress distribution is important to improve the roll fatigue life due to the compressive residual stress at the roll surface. Recently, to reduce the tensile residual stress appearing at the roll center, quenching heat treatment is performed just after heating the roll non-uniformly instead of heating the roll uniformly with enough time. In this paper, therefore, the residual stresses are compared after between the uniform heating quenching and the non-uniform heating quenching on the basis of the FEM simulation. The results show that tensile stresses at the roll center for non-uniform heating are smaller than that for uniform heating by 400MPa although the same compressive stresses appear at the surface. The effect of creep on stress relaxation is also considered in this study. By considering creep, the maximum tensile residual stress decreases by 8% for uniform heating and by 15% for non-uniform heating

Residual stress generation mechanism for hot strip composite rolls during quenching process

Composite rolls are widely used in hot rolling mill because of the excellent hardness, wear resistance and high temperature properties. During hot rolling process, composite rolls are subjected to heating-cooling thermal cycles from the hot strip contact and water cooling. The thermal stress is added to already existing residual stress. The thermal fatigue cracking appears at roll surface, and the fracture is possible happen in roll centre when the tensile stress exceeds the centre strength. Therefore, residual stress plays an important role in composite roll. In this paper, FEM (finite element method) simulation is performed to investigate the generation mechanism of the residual stress during quenching process. It should be notedthat a large number of experimental data of the core and shell materials are utilized for the wide range oftemperature considering the quenching process. The results verify that initially the tensile stress appears on the roll surface but finally the compressive stress occurs.Proceedings of 4th International Conference on Fracture Fatigue and Wear, FFW 2015, Ghent University, Belgium, 27-28 August 201

Deep Learning Methods for Underwater Target Feature Extraction and Recognition

The classification and recognition technology of underwater acoustic signal were always an important research content in the field of underwater acoustic signal processing. Currently, wavelet transform, Hilbert-Huang transform, and Mel frequency cepstral coefficients are used as a method of underwater acoustic signal feature extraction. In this paper, a method for feature extraction and identification of underwater noise data based on CNN and ELM is proposed. An automatic feature extraction method of underwater acoustic signals is proposed using depth convolution network. An underwater target recognition classifier is based on extreme learning machine. Although convolution neural networks can execute both feature extraction and classification, their function mainly relies on a full connection layer, which is trained by gradient descent-based; the generalization ability is limited and suboptimal, so an extreme learning machine (ELM) was used in classification stage. Firstly, CNN learns deep and robust features, followed by the removing of the fully connected layers. Then ELM fed with the CNN features is used as the classifier to conduct an excellent classification. Experiments on the actual data set of civil ships obtained 93.04% recognition rate; compared to the traditional Mel frequency cepstral coefficients and Hilbert-Huang feature, recognition rate greatly improved

Phase transition mechanism and bandgap engineering of Sb2S3 at gigapascal pressures

Earth-abundant antimony trisulfide (Sb2S3), or simply antimonite, is a promising material for capturing natural energies like solar power and heat flux. The layered structure, held up by weak van-der Waals forces, induces anisotropic behaviors in carrier transportation and thermal expansion. Here, we used stress as mechanical stimuli to destabilize the layered structure and observed the structural phase transition to a three-dimensional (3D) structure. We combined in situ x-ray diffraction (XRD), Raman spectroscopy, ultraviolet-visible spectroscopy, and first-principles calculations to study the evolution of structure and bandgap width up to 20.1 GPa. The optical band gap energy of Sb2S3 followed a two-step hierarchical sequence at approximately 4 and 11 GPa. We also revealed that the first step of change is mainly caused by the redistribution of band states near the conduction band maximum. The second transition is controlled by an isostructural phase transition, with collapsed layers and the formation of a higher coordinated bulky structure. The band gap reduced from 1.73 eV at ambient to 0.68 eV at 15 GPa, making it a promising thermoelectric material under high pressure

Simulation of thermal stress and fatigue life prediction of high speed steel work roll during hot rolling considering the initial residual stress

Considerable residual stress is produced during heat treatment. Compressive residual stress at the shell is conductive to improving the thermal fatigue life of a work roll, while tensile stress in the core could cause thermal breakage. In hot rolling, thermal stress occurs under the heating-cooling cycles over the roll surface due to the contact with the hot strip and water spray cooling. The combination of thermal stress and residual stress remarkably influences the life of a work roll. In this paper, finite element method (FEM) simulation of hot rolling is performed by treating the residual stress as the initial stress. Afterwards, the effects of the initial roll temperature and cooling conditions on thermal stress considering the initial residual stress are discussed. Lastly, the thermal fatigue life of a work roll is estimated based on the strain life model. The higher initial roll temperature causes a higher temperature but a lower compressive thermal stress at the roll surface. The surface temperature and compressive stress increase significantly in the insufficient cooling conditions, as well as the center tensile stress. The calculation of the fatigue life of a work roll based on the universal slopes model according to the 10% rule and 20% rule is reasonable compared with experimental results

Improved rheology and high-temperature stability of hydrolyzed polyacrylamide using graphene oxide nanosheet

Hydrolyzed polyacrylamide (HPAM) is a polymer that extensively used in chemical industry and hydrocarbon extraction and refinery processes, but suffers a common problem of high-temperature instability. This study improved high-temperature rheological characteristics of HPAM by using novel graphene oxide (GO) nanosheets. Stable GO dispersions in aqueous HPAM were formulated, and their dynamic and viscoelastic behaviors were studied. The results showed that the addition of GO significantly increased the viscosities and high-temperature stability of the base polymer fluid, as well as the elastic properties of the dispersion. Spectral data indicated the formation of covalent linkages and electrostatic hydrogen bonding between the GO and the HPAM functional groups, leading to enhanced stability and viscosity that is beneficial for high-temperature oil recovery. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47582