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Abstract This paper was dealt with buckling and post-buckling behavior of short thin-walled Z-columns made of a carbon-epoxy laminate, subjected to eccentric compressive load. The buckling mode and the buckling load of real structures versus load eccentricity were discussed. The study involved both experimental tests were carried out on real laminated structures and numerical simulations by the finite element method. The buckling load of real structures was determined by approximation methods on the basis of experimental and numerical post-buckling equilibrium paths of the structure. Additionally, in numerical simulations, the bifurcation load value was determined by solving an eigen problem. In all cases, experimental findings and numerical results show high agreement. The study determined the quantitative influence of the direction and value of compressive load eccentricity on the buckling load and rigidity of the structure in the post-buckling state. [ABSTRACT FROM AUTHOR]

In this paper, collapse properties of the capped-end cone tubes made from steel alloy 430 with circular holes under quasi-static axial loading have been studied experimentally and numerically. Simulations were performed using finite element LS-Dyna software and 11 types of cone with various number of holes (3, 4 and 5) and heights (20,40 and 60 mm relative to bottom base of cone) in four different thicknesses (0.2, 0.4, 0.6 and 1 mm), so, 44 different states were totally simulated and the collapse properties of them were extracted. The samples with the thickness of 0.2 mm were tested on an experimental basis in order to ensure the accuracy of the simulation results. Comparing the obtained results indicates good agreement between the experimental and numerical data. According to the obtained results, it was found that open end absorbers are more efficient compared to similar capped-end structures. Also, it was revealed that creating holes in the capped-end cone decreases the maximum force and increases crush force efficiency. In addition, it was found that creating hole farther away from the underlying base is more effective for improving the collapse properties. In the final section, the effects of thickness on the collapse properties were evaluated. The obtained results in this study can be a good guidance for investigation on the effect of discontinuity on collapse properties. [ABSTRACT FROM AUTHOR]

In this paper, the recent development of extended consecutive-interpolation 4-node quadrilateral element (XCQ4), which goes beyond certain limitations of conventional methods, is further employed to study dynamic and static thermoelastic fracture problems. In particular, static stress intensity factors (SIFs) and transient dynamic responses of two-dimensional (2-D) stationary cracks in elastic solids under thermal and thermal-mechanical loadings are investigated. In addition, simulation of quasi-static crack propagation under thermal-mechanical loading condition is also performed. To precisely capture the singularity and discontinuity of temperature, heat flux, and displacements due to the presence of crack, the unknown field variables of mechanical displacements and temperature are approximated in terms of the XCQ4 framework by different enrichment strategies, which include either the use of the conventional branch functions or the new ramp function associated with Heaviside function. Only adiabatic condition is considered on the crack surfaces. For quasi-static crack growth analysis, the maximum hoop stress criterion, which is also valid for thermo-elastic fracture mechanics, is adopted. For transient crack analyses, the inertial effect is taken into account for the interaction integral in the consideration of DSIFs. Through eight numerical examples for thermoelastic fracture problems, the validity of the XCQ4 is confirmed by a comparison of the obtained results to those derived from different approaches in previous studies. In addition, the accuracy, performance, and superior advantages of the XCQ4 over standard extended finite element approach are also demonstrated. [ABSTRACT FROM AUTHOR]

In this paper, the gas tungsten-arc welding (GTAW) process of a thin cylinder made of Al6061-T6 alloy was simulated using 3-D finite element model in the ABAQUS code and the induced distribution of residual stress was obtained. Temperature dependent thermo-mechanical properties were considered for the aluminum alloy and for simulating the heat source of tungsten arc welding; Goldak's double ellipsoid model was employed. The numerical simulation method employed for the GTAW process of investigated aluminum material was validated experimentally using the hole drilling method as well. High residual stresses were found around the weld line and HAZ area which can increase the risk of crack initiation and propagation in this region of welded aluminum cylinder. Hence in the second part of this research, a longitudinal semi-elliptical crack was considered in the wall of aluminum cylinder subjected to combined internal pressure and torsional loads and its mixed mode I/II fracture parameters (i.e. K I , K II and T ) were determined numerically along the crack front and for different crack geometries. Finally the influence of obtained residual stress field on the computed fracture parameters was reanalyzed using the coupled residual stress/mechanical loading applied to the cylinder. The residual stress field had no effect on the mode II fracture component but the most influence of this factor was observed for mode I stress intensity factor ( K I ) and the deepest point of 3D elliptical crack. [ABSTRACT FROM AUTHOR]

This paper deals with the investigation of a numerical simulation method to appropriately represent relevant failure mechanisms of carbon fiber reinforced plastic (CFRP) components subjected to dynamic crash loads. The presented work considers the stacked shell approach, using a stack of continuum shell elements and cohesive elements, and focuses on the calibration of simulation input parameters. Furthermore, modeling aspects are discussed to reduce mesh-dependencies for the simulation of progressive crushing. The validation of the numerical approach is performed on the basis of an extensive test program of CFRP crush absorbers on the structural level. The capability of current state-of-the-art technologies for the simulation of progressive crushing is identified. The simulations capture general failure effects and force-displacement characteristics for different designs and loading conditions. Drawbacks are identified in the definition of cohesive input parameters to obtain numerical stability for complex loading conditions. The numerical simulations were performed using the commercial finite element software Abaqus/Explicit. [ABSTRACT FROM AUTHOR]

This paper presents a detailed investigation about the geometric non-linear stiffness behavior of corrugated laminates in six different load cases. The considered tensile, bending, and shear load cases allow the modeling with a unit-cell approach assuming a generalized plane strain state. The torsional load case is more complex. There the mechanical response depends on the number of unit-cells and the width of the samples in case of geometric non-linearities. We first identify the load cases that show a non-linear stiffness response under large deformation. Then the non-linear behavior is analyzed in detail using numerical simulation and we aim for mechanical explanations to describe the non-linear behavior. The FE simulations of the torsional load case are validated using experiments with 3D printed samples. [ABSTRACT FROM AUTHOR]

Ground overload is one of the most important factors that threaten the safe operations of oil and gas pipelines. The mechanical behaviour of a buried pipeline under ground overload was investigated using the finite element method in this paper. The effects of the overload parameters, pipeline parameters and surrounding soil parameters on the stress–strain response of the buried pipeline were discussed. The results show that the maximum von Mises stress appears on the top of the buried pipeline under the loading area when the ground load is small, and the stress distribution is oval. As the ground load increases, the maximum stress increases, and the high stress area extends. The von Mises stress, plastic strain, plastic area size, settlement and ovality of the buried pipeline increase as the ground load and loading area increase. The buckling phenomenon of the no-pressure buried pipeline is more serious than the pressure pipeline. As the internal pressure increases, the high stress area and the maximum plastic strain of the buried pipeline first decrease and then increase, the settlement of the buried pipeline increases, and the ovality decreases. The von Mises stress, maximum plastic strain, settlement and ovality of the buried pipeline decrease with increasing buried depth, the surrounding soil's elasticity modulus, Poisson's ratio and cohesion. The maximum von Mises stress, high stress area, the maximum plastic strain, plastic area and ovality increase as the diameter–thickness ratio increases. The critical diameter–thickness ratio is 60, and the settlement of the buried pipeline first increases and then decreases as the diameter–thickness ratio increases. Finally, a protective device of the buried pipeline is designed for preventing ground overload. It can be repaired in a timely manner without stopping the transmission of oil and gas and widely used in different locations because of its simple structure and convenient installation. [ABSTRACT FROM AUTHOR]

With its advantages of lost circulation prevention, drilling speed improvement and reservoir protection, gas drilling technology has been widely applied in Sichuan and Xinjiang oilfields in China . However, drill collar failures have often occurred under high weight on bit (WOB) during gas drilling. These incidents have not only caused serious economic loss but hampered the development and application of gas drilling. Finite element analysis is used to determine the drill collar thread stress distribution and, using simulation of drill string dynamics, multi-axial fatigue life theory is used to calculate the life of a standard API drill collar connection. The computed results reveal the early drill collar fatigue failures in gas drilling. Then, the multi-axial fatigue life of drill collar with double shoulder thread is analyzed under the same loads. Analysis shows that the fatigue life of a double shoulder thread is some thirty times that of the API thread. So drill collar with double shoulder thread could be an efficient way to solve the fatigue failure problems of drill collar in gas drilling. The work presented in this paper can provide theoretical foundations for safe and efficient drilling with gas. [ABSTRACT FROM AUTHOR]

In this paper, the buckling response of glass panels linearly supported along the top and bottom edges, under the action of in-plane shear loads, is investigated by means of analytical and Finite-Element (FE) methods. The typical buckling behaviour is first assessed in the hypothesis of fully neglecting the possible deformability contribution of adhesive linear supports, while successively the effects of linear, flexible sealant joints on the overall structural response of the same panels are also properly taken into account and highlighted. Based on extended parametric FE linear buckling and nonlinear incremental simulations, the influence of initial geometrical imperfections with various shapes and amplitudes, adhesive stiffnesses and glass types is investigated, both for monolithic and laminated glass panels. In the latter case, the accuracy of an equivalent thickness approach derived from early contributions is also demonstrated. Analytical approximating curves are proposed for the fitting of numerically derived buckling coefficients, so that they could represent a practical tool in the calculation of the expected Euler’s critical load. A normalized buckling curve for ideally simply supported glass panels under in-plane shear loads is finally recalled from past research projects and proposed as a rational design method for the examined loading and boundary condition. [ABSTRACT FROM AUTHOR]

This paper is to develop a simple micromechanics-based model taking account of progressive damaging for carbon black (CB) filled rubbers. The present model constitutes of the instantaneous Young's modulus and Poisson's ratio characterizing rubber-like material, a double-inclusion (DI) configuration considering the absorption of rubber chains onto CB particles, and the incremental Mori-Tanaka formula to compute the effective stress–strain relations. The progressive damage in filled rubbers is described by the DI cracking, which is represented by the remaining load–carrying capacity. The present predictions are capable of embodying the well-known S -shaped response of filled rubbers, and also verified by the comparison with the experimental and analytical results. Moreover, strain localization effect is clearly demonstrated by finite element method (FEM) simulations, and reaches a decisive interpretation to the complicated synergic micro-mechanisms between hard fillers and soft phase in such flexible composites. [ABSTRACT FROM AUTHOR]

The present paper aims at investigating the homogenisation of cellular materials in view of the modelling of large but finite cellular structures. Indeed, computation costs associated with the complete modelling of such structures can be rapidly prohibitive if industrial applications are considered. The use of a homogeneous equivalent medium (HEM) for these cellular materials can be an efficient approach to address this issue, but it requires the calibration of relevant homogeneous equivalent laws (HELs). Here, the considered cellular materials are tube stackings. Various uni-axial and multi-axial loading cases have been simulated, through the finite element method, on representative volume elements of such periodic stackings. From these simulations, anisotropic compressible elasto-plastic constitutive equations have been identified for the HEL. The anisotropy of the yield surfaces is discussed depending on the pattern of the tube stacking (e.g. square or hexagonal). A validation of the identified laws is proposed by simulating uni-axial compression and simple shear tests on sandwich structures made of tube stackings for their cores. A systematic comparison, between the results obtained from the fully meshed structures and those obtained from the structures whose core has been replaced with its HEM, allows us to address the limitations of the HEM-based approach and the boundary layer effects observed on finite structures. [ABSTRACT FROM AUTHOR]