Geometric and material nonlinear analysis of tensegrity structures

A numerical method is presented for the large deflection in elastic analysis of tensegrity structures including both geometric and material nonlinearities.The geometric nonlinearity is considered based on both total Lagrangian and updated Lagrangian formulations,while the material nonlinearity is treated through elastoplastic stress-strain relationship.The nonlinear equilibrium equations are solved using an incremental-iterative scheme in conjunction with the modified Newton-Raphson method.A computer program is developed to predict the mechanical responses of tensegrity systems under tensile,compressive and flexural loadings.Numerical results obtained are compared with those reported in the literature to demonstrate the accuracy and efficiency of the proposed program.The flexural behavior of the double layer quadruplex tensegrity grid is sufficiently good for lightweight large-span structural applications.On the other hand,its bending strength capacity is not sensitive to the self-stress level.

Forecasting Damage Mechanics By Deep Learning

We in this paper exploit time series algorithm based deep learning in forecasting damage mechanics problems.The methodologies that are able to work accurately for less computational and resolving attempts are a significant demand nowadays.Relied on learning an amount of information from given data,the long short-term memory(LSTM)method and multi-layer neural networks(MNN)method are applied to predict solutions.Numerical examples are implemented for predicting fracture growth rates of L-shape concrete specimen under load ratio,single-edge-notched beam forced by 4-point shear and hydraulic fracturing in permeable porous media problems such as storage-toughness fracture regime and fracture-height growth in Marcellus shale.The predicted results by deep learning algorithms are well-agreed with experimental data.

薄壁组合箱梁的自由振动

研究薄壁叠加组合梁的自由振动。建立了适用于薄壁组合箱梁截面动力性能的一般分析模型。该模型基于古典叠加理论,考虑任意层压板叠合次序情况下弯曲和扭转的耦合,也就是非对称和对称以及各种边界条件。对薄壁组合梁,建立基于位移的一维有限元模型以预测自振频率和相应的振型,并由Hamilton原理派生出运动方程;考虑薄壁组合梁纤维角度、模数比、振动频率的边界条件以及组合形式的影响,得出计算结果。

薄壁复合箱型梁的弯曲-扭转屈曲分析

对一轴心受压薄壁复合构件的屈曲进行研究。提出一个广义的分析模型,可用于分析轴心受压薄壁复合箱型梁的弯曲、扭转以及弯扭屈曲作用。此模型基于经典层压理论,考虑了任意层压堆积规律,结构的弯曲和扭转模式的耦合问题,如非对称以及对称和各种边界条件。采用一个基于位移的一维有限元模型来预测薄壁复合钢筋的临界荷载和随后的屈曲模式。从总势能的平稳值原则中推导出屈曲控制方程。轴心受压薄壁复合件的数值计算结果可用于估测纤维角、各向异性和边界条件对临界屈曲荷载和复合件模态的影响。

Improving hydroxyapatite coating ability on biodegradable metal through laser-induced hydrothermal coating in liquid precursor:Application in orthopedic implants

During the past decade,there has been extensive research toward the possibility of exploring magnesium and its alloys as biocompatible and biodegradable materials for implantable applications.Its practical medical application,however,has been limited to specific areas owing to rapid corrosion in the initial stage and the consequent complications.Surface coatings can significantly reduce the initial corrosion of Mg alloys,and several studies have been carried out to improve the adhesion strength of the coating to the surfaces of the alloys.The composition of hydroxyapatite(HAp)is very similar to that of bone tissue;it is one of the most commonly used coating materials for bone-related implants owing to favorable osseointegration post-implantation.In this study,HAp was coated on Mg using nanosecond laser coating,combining the advantages of chemical and physical treatments.Photothermal heat generated in the liquid precursor by the laser improved the adhesion of the coating through the precipitation and growth of HAp at the localized nanosecond laser focal area and increased the corrosion resistance and cell adhesion of Mg.The physical,crystallographic,and chemical bondings were analyzed to explore the mechanism through which the surface adhesion between Mg and the HAp coating layer increased.The applicability of the coating to Mg screws used for clinical devices and improvement in its corrosion property were confirmed.The liquid environment-based laser surface coating technique offers a simple and quick process that does not require any chemical ligands,and therefore,overcomes a potential obstacle in its clinical use.

Regulation of cell locomotion by nanosecond-laser-induced hydroxyapatite patterning

Hydroxyapatite,an essential mineral in human bones composed mainly of calcium and phosphorus,is widely used to coat bone graft and implant surfaces for enhanced biocompatibility and bone formation.For a strong implant-bone bond,the bone-forming cells must not only adhere to the implant surface but also move to the surface requiring bone formation.However,strong adhesion tends to inhibit cell migration on the surface of hydroxyapatite.Herein,a cell migration highway pattern that can promote cell migration was prepared using a nanosecond laser on hydroxyapatite coating.The developed surface promoted bone-forming cell movement compared with the unpatterned hydroxyapatite surface,and the cell adhesion and movement speed could be controlled by adjusting the pattern width.Live-cell microscopy,cell tracking,and serum protein analysis revealed the fundamental principle of this phenomenon.These findings are applicable to hydroxyapatite-coated biomaterials and can be implemented easily by laser patterning without complicated processes.The cell migration highway can promote and control cell movement while maintaining the existing advantages of hydroxyapatite coatings.Furthermore,it can be applied to the surface treatment of not only implant materials directly bonded to bone but also various implanted biomaterials implanted that require cell movement control.

Damage Identification of Truss Structures Based on Force Method

An computationally efficient damage identification technique for the planar and space truss structures is presented based on the force method and the micro ge-netic algorithm.For this purpose,the general equilibrium equations and the kinematic relations in which the reaction forces and the displacements at nodes are take into ac-count,respectively,are formulated.The compatibility equations in terms of forces are explicitly presented using the singular value decomposition(SVD)technique.Then governing equations with unknown reaction forces and initial elongations are derived.Next,the micro genetic algorithm(MGA)is used to properly identify the site and ex-tent of multiple damage cases in truss structures.In order to verify the accuracy and the superiority of the proposed damage detection technique,the numerical solutions are presented for the planar and space truss models.The numerical results indicate that the combination of the force method and the MGA can provide a reliable tool to accurately and efficiently identify the multiple damages of the truss structures.

Stability for Leipholz’s Type of Laminated Box Columns with Nonsymmetric Lay-Ups on Elastic Foundation

The stability behavior of the Leipholz’s type of laminated box columns with nonsymmetric lay-ups resting on elastic foundation is investigated using thefinite el-ement method.Based on the kinematic assumptions consistent with the Vlasov beam theory,a formal engineering approach of the mechanics of the laminated box column-s with symmetric and nonsymmetric lay-ups is presented.The extended Hamilton’s principle is employed to obtain the elastic stiffness and mass matrices,the Rayleigh damping and elastic foundation matrices,the geometric stiffness matrix due to dis-tributed axial force,and the load correction stiffness matrix accounting for the uni-formly distributed nonconservative forces.The evaluation procedures for the critical values of divergence andflutter loads with/without internal and external damping ef-fects are briefly presented.Numerical examples are carried out to validate the present theory with respect to the previously published results.Especially,the influences of thefiber angle change and damping on the divergence andflutter loads of the laminated box columns are parametrically investigated.