Thin-walled Metallic Structures Research Articles

Localization of inhomogeneities in an elastic plate using the time reversal method

Theoretical and practical aspects of applying time reversal of elastic waves to localize a source of oscillations or a defect are considered in problems of active ultrasonic monitoring of thin-walled metal structures. Backward reradiation of a time-reversed signal is implemented using a computer model based on a semianalytical integral approach. The proposed algorithm is verified experimentally on aluminum samples excited by piezoelectric wafer active sensors. The results corroborate the possibility of reliably determining of the position and size of the load application region and a local inhomogeneity with a relatively small number of signal measurement points on the sample surface.

Manufacture of complex thin-walled metallic objects using weld-deposition based additive manufacturing

Gas Metal Arc Welding (GMAW) based weld-deposition process is one of the deposition-based Additive Manufacturing (AM) processes with the ability to produce fully dense complex functional metallic objects. Due to its high deposition rates, high material and power efficiency, lower investment costs, simpler setup and work environment requirements it is slowly becoming a viable metallic AM method. Amongst various geometrical features that can be realized in weld-deposition based AM, the thin-walled features (i.e., features with one single deposition pass) are the toughest as the process has to overcome the bead-over-bead complexity. Based on geometric modelling and experimentation, this paper presents an efficient technique for producing the thin-walled metallic structures, including objects with undercut features. This is possible by adding extra degrees of freedom or by using higher order kinematics to the work piece and/or to the deposition head by suitably aligning the overhanging feature in-line to the deposition direction. An in-house MATLAB code was developed to slice the CAD model and generate the tool path for inclined deposition of a given layer of a thin-walled model. A geometrical model proposed to predict the layer thickness of a given layer during such bead-on-bead deposition showed good correlation with experimental data. Some illustrative complex thin-walled components successfully fabricated using this model have also been presented.

Predicting indenter nose shape sensitivity for quasi-static perforation of thin metallic plates

Perforation resistance is an important design consideration for thin-walled metallic structures. However, the perforation energy of thin metallic plates is known to be sensitive to the nose shape of the indenter. This poses a challenge for predictive modelling, both analytical and numerical, as the material deformation and state of stress at the onset of failure can vary significantly from one indenter geometry to the next. Effective design requires an understanding of the key modelling parameters, and their influence on the predicted perforation response, across the widest range of possible indenter geometries. This paper aims to investigate systematically the indenter nose shape sensitivity of the quasi-static perforation of a 1 mm thick plate of aluminium alloy 6082-T4, and the modelling of the conditions at failure. The nose shape of the indenter is gradually changed from flat (i.e. blunt) to hemi-spherical either by (i) introducing a chamfer at the edge of the indenter or (ii) by changing the indenter frontal nose radius. This allows a wide range of states of deformation at the onset of failure to be spanned. The problem is investigated by both analytical and numerical methods. The results of both modelling techniques are compared with quasi-static perforation experiments, and the conditions necessary to achieve good agreement are obtained. Careful consideration of (i) material anisotropy, (ii) indenter-plate friction and (iii) boundary compliance is necessary for accurate prediction of the perforation energy. A Lode angle-dependent model for the onset of failure in the metal is found to be essential for predicting the perforation response for a range of indenter chamfer radii.

Composite energy-absorbing structures combining thin-walled metal and honeycomb structures

The energy-absorbing structure of a crashworthy railway vehicle was designed by combining the characteristics of thin-walled metal structures and aluminum honeycomb structures: finite element models of collisions involving energy-absorbing structures were built in ANSYS/LS-DYNA. In these models, the thin-walled metal structure was modeled as a plastic kinematic hardening material, and the honeycomb structure was modeled as an equivalent solid model with orthotropic–anisotropic mechanical properties. The analysis showed that the safe velocity standard for rail vehicle collisions was improved from 25 km/h to 45 km/h by using a combined energy-absorbing structure; its energy absorption exceeded the sum of the energy absorbed by the thin-walled metal structure and honeycomb structure when loaded separately, because of the interaction effects of thin-walled metal structure and aluminum honeycomb structure. For an aluminum honeycomb to the same specification, the composite structure showed the highest SEA when using a thin-walled metal structure composed of bi-grooved tubes, followed by that using single-groove tubes: that with a straight-walled structure had the lowest SEA.

Free vibration analysis of simply supported beams with solid and thin-walled cross-sections using higher-order theories based on displacement variables

Solutions for undamped free vibration of beams with solid and thin-walled cross-sections are provided by using refined theories based on displacement variables. In essence, higher-order displacement fields are developed by using the Carrera unified formulation (CUF), and by discretizing the cross-section kinematics with bilinear, cubic and fourth-order Lagrange polynomials. Subsequently, the differential equations of motion and the natural boundary conditions are formulated in terms of fundamental nuclei by using CUF and the strong form of the principle of virtual displacements. The second-order system of ordinary differential equations is then reduced into a classical eigenvalue problem by assuming simply supported boundary conditions. The proposed methodology is extensively assessed for different solid and thin-walled metallic beam structures and the results are compared with those appeared in published literature and also checked by finite element solutions. The research demonstrates that: (i) the innovative 1D closed form CUF represents a reliable and compact method to develop refined beam models with solely displacement variables; (ii) 3D-like numerically exact solutions of complex structures can be obtained with ease; and (iii) the numerical efficiency of the present method is uniquely robust when compared to other methods that provide similar accuracies.

Сrack Branching in Catastrophic Fractures of Metal Structures and Environmental Damages

A B S T R A C T In this article, fracturing in large-scale metal structures such as main gas pipelines, fuel and oil tanks operated in Arctic were investigated. It is shown that catastrophic accidents involved in large thinwalled metal structures in large diameter pipelines, tanks and pressure vessels. The fractures occurred not only due to stretch propagation of brittle or viscous fractures, but also followed branching that leads to fragmented fractures with simultaneous movement of many cracks. The character of the fracture depends on the level of the fracture strength. At high levels cracks propagated at a high speed by a mechanism of separation; as a result of crack branching fragment damage occurred. At low level, cracks propagate at a low speed by a cutting mechanism; that does not cause extensive fracturing. The cracks may cause structural and environmental damages.

Novel Design of Impact Attenuator for an 'Eco Challenge' Car

Thin-walled metallic tubular structures are generally used as impact energy absorber in automotive structures due to their ease of fabrication and installation, high energy absorption capacity and long stroke. However, unlike a normal passenger car where the impact energy can be distributed throughout the whole structure, the impact energy absorbing system of an Eco-Challenge car is confined within a limited space on the front bulkhead. The challenge is to develop an impact attenuator system that can effectively absorb the impact energy within the given space and fulfil the specified rate of deceleration. This new design utilized the standard Aluminium 6063 circular tubes, cut and welded into specific configurations i.e. stacked toroidal tubes with central axial tube sandwiched between two flat plates. Two configurations were investigated; circular and square toroids. Explicit non-linear FEA software was used to determine the impact response i.e. energy absorption, impact force and rate of deceleration. Both configurations showed promising results but the configuration that can be readily fabricated was chosen as the final design.

EFFECTS OF CFRP REINFORCEMENTS ON THE BUCKLING BEHAVIOR OF THIN-WALLED STEEL CYLINDERS UNDER COMPRESSION

This paper presents a novel way of strengthening thin-walled steel cylindrical shells against buckling during axial compression in which a small amount of fiber-reinforced polymer (FRP) composite, coated from both sides can increase the buckling strength effectively. The effects of the reinforcement and the angle of fiber orientation as well as initial geometric imperfections on the buckling load-carrying capacity have been made clear through the three kinds of analytical procedures; the conventional linear eigen value buckling analysis, the reduced stiffness (RS) buckling analysis and the fully nonlinear numerical experiments. These multiple treatments suggest obtaining valuable information for the design of FRP-based hybrid structural elements and discusses influence of FRP to increase the load-carrying capacity of the thin-walled metallic structures having complex buckling collapse behavior. This paper also discusses how the angle of fiber orientation affects on the buckling strength and the associated buckling modes of the thin-walled shells.

Enhanced Acoustic Emission Detection Induced by Electromagnetic Stimulation With External Magnetic Field

This paper introduces a new electromagnetically induced acoustic emission technology (EMAE) enhanced by an external magnetic field. The external magnetic field generated by Nd-Fe-B magnet can improve the ability of detecting the defects, due to the even bigger deformation generated by the enhanced Lorentz Force. In this paper, the finite-element model of EMAE including an external magnetic field has been implemented in accordance with the practical experiment models. The sample's deformation has been analyzed when the exciting coil locates at different positions. The experiment of EMAE is built according to the finite-element analysis (FEA) results. Experiments' outcomes indicate that the defect itself can generate modulated acoustic emission signals, which could be used to boost the detection ability of small cracks in the thin-walled metallic structures.

Electromagnetic Stimulation of the Acoustic Emission for Fatigue Crack Detection of the Sheet Metal

A new electromagnetically induced acoustic emission technique (EMAE) is presented in this paper. Due to the acoustic emission signal generated by the electromagnetically induced high-density eddy current pulse, EMAE can locate small flaws or cracks in thin-walled structures nondestructively in order to inspect specific areas without loading the whole structure. The acoustic emission (AE) signal captured by conventional or fiber optic AE sensors is modulated at the defect due to the crack closure. The differences can be found by comparing modulated AE signals from the defects and ones from the intact region in the spectrum. In this paper, the finite element model of EMAE has been implemented based on the concrete experiment models. The sample's deformation has been analysed when the exciting coil locates at different position. The results of experiments indicate that electromagnetic transient modulation of the acoustic emission could be used to enhance detection of small cracks in thin-walled metallic structures.

Electromagnetic Stimulation of the Ultrasonic Signal for Nondestructive Detection of Ferromagnetic Inclusions and Flaws

In this paper, the method of nondestructive detection based on electromagnetic modulation of the ultrasonic signal scattered from the inclusions or defects has been reported. The electromagnetically induced high-density current pulse generates transient stress fields which alter the ultrasonic waves scanning the part with the defect and modulate the ultrasonic signal due to magnetoelastic coupling, magnetostriction, or the crack closure effect. The results of applying electromagnetic transient modulation of the ultrasonic echo pulse tone-burst suggest that this method could be used to enhance detection of small cracks and ferromagnetic inclusions in thin-walled metallic structures.

Accuracy and adaptivity in the numerical analysis of thin-walled structures

An integrated concept for more accurate robust and reliable FE-computations of thin-walled metal structures with elasto-plastic large deformations subject to static loads is presented. It includes adaptive mesh refinement using a priori and posteriori criteria and the use of a multigrid solver. We have developed a mesh refinement procedure that allows the combination of mesh adaptation and multigrid methods for arbitrarily complex structures. Illustrated examples for a priori and a posteriori mesh refinements are included.

Thin-walled metal structures in buildings

Thin-walled metal structures in buildings

Thin-walled metal structures in building- Stockholm, Sweden, June 9–12, 1986

Thin-walled metal structures in building- Stockholm, Sweden, June 9–12, 1986