Thin-walled Model Research Articles

Behavior of ring-restrained high-performance concrete under extreme heating and development of screening test

This study evaluated the behavior of restrained high-performance concrete in response to the extreme heating associated with fire. This was done by estimating the thermal stress based on the strain induced in the restraining steel ring and the vapor pressure in the restrained concrete under the conditions corresponding to the RABT 30 rapid heating curve. The thermal stress was calculated based on the thin-wall cylinder model theory. A spalling failure model based on a tensile strain failure model was proposed. The results indicated that the model was suitable for determining the spalling initiation point as well as the spalling depth.

Energy absorption of thin-walled profiles made of AZ31 magnesium alloy

The paper compares the energy absorption of the AZ31 magnesium alloy with the DC04 and HC380LA steel on the example of the thin-walled model profiles made by the process of bending. Additionally, the studies involved the application of aluminium foam filling the sections in order to increase their energy absorption.The first stage of the research included the elaboration of a technology of producing the thin-walled model profiles from a magnesium alloy by way of bending, with the use of tools heated to 270°C and 300°C. Next, the prepared sections halves were joined with the use of the FSW method. The static tensile tests showed that the FSW joints underwent damage in the native material or at the boundary with the heat-affected zone, which confirmed their high strength.The main aim of the use of the magnesium alloy was to lower the mass of the bodywork. And so, in order to compare the energy absorption of the profiles made of steel with those made of magnesium alloys, the mass of the samples should be taken into consideration. To that end, in the study, the parameter of specific energy absorption was introduced, which is the absorbed energy divided by the mass of the sample. The dynamic deformation tests performed on the profiles made of the AZ31 magnesium alloy and the DC04 and HC380LA steel demonstrated that the profiles made of only the AZ31 magnesium, due to their low deformability, do not exhibit sufficient energy absorption. In order to increase it, hybrid samples should be applied. The study proposed filling the profiles made of the AZ31 alloy with aluminium foam. This caused their specific energy absorption to be higher than that of the steel profiles.

Transition due to Roughness on Blunt Capsule: Comparison with Transient Growth Correlation

The effect of uniformly distributed surface roughness on the onset of boundary-layer transition for a capsule geometry was experimentally investigated in a conventional hypersonic blowdown wind tunnel. The thin-walled scale model of the Orion Crew Exploration Vehicle used in this study was mounted at a 28 deg angle of attack in the Adjustable Contour Expansion wind tunnel. A test matrix of 24 runs was developed to experimentally estimate the location of transition and to relate the flow properties at this location and the roughness height to established transient growth scaling. Tests were conducted for four different Reynolds numbers at six quasi-uniform surface roughness height distributions. The tunnel was nominally set to Mach 6.0 and a total temperature of 430 K for each run. Infrared thermometry was used to measure the surface temperature distribution. Heat transfer rates generated through a series of surface temperature maps were processed into normalized Stanton number centerline plots. These plots directly indicated the boundary-layer transition location. Analysis of the results indicated that the experimental data matched the established transient growth scaling.

Investigation of coupled instability for shear flexible FG sandwich I-beams subjected to variable axial force

The general thin-walled beam model is presented to study the flexural-torsional coupled buckling behavior of shear flexible sandwich I-beams made of functionally graded materials based on an orthogonal Cartesian coordinate system. The derived beam model includes the transverse shear, the restrained warping induced shear deformations, the structural coupling coming from the material anisotropy, and the variable axial force effect. Material properties of the beam such as Young’s and shear moduli are assumed to be graded across the wall thickness. The strain energy and the potential energy due to the variable axial force are introduced. The seven coupled instability equations are derived from the energy principle. To solve the instability problem, three types of finite beam elements, namely, linear, quadratic, and cubic elements are employed with the scope to discretize the governing equations. In order to verify the accuracy and efficiency of the beam model presented by this study, numerical results are presented and compared with results from other researchers. By numerical examples, the bisymmetric and mono-symmetric I-beams with two types of material distributions are considered to investigate the effects of shear deformation, variable axial force, gradient index, thickness ratio of ceramic, boundary conditions, material ratio, and span-to-height ratio on the buckling behavior of FG sandwich I-beams. Particularly, the crossover phenomenon in buckling modes with changes in gradient index and thickness ratio of ceramic in flanges is investigated.

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.

Improved formulation for spatial free vibration of thin-walled Al/Al2O3 FG sandwich beams with non-symmetric open, single- and double-cell sections

In this study, an improved formulation is presented for the spatially coupled free vibration analysis of Al/Al2O3 thin-walled functionally graded (FG) sandwich beams with non-symmetric open, single- and double-cell sections. The thin-walled beam model is based on the Euler-Bernoulli beam theory for bending and the Vlasov theory for torsion. The FG beam consists of ceramic (Al2O3) and metal (Al) phases varying through the wall thickness. Three types of material distribution, which leads to the material coupling, are considered. The strain and kinetic energies are derived by introducing displacement parameters defined at the arbitrary chosen axis considering the effects of axial-flexural-torsional coupling and restrained warping. For finite element analysis, cubic polynomials are utilized as the shape functions of two-noded Hermitian beam element. Elastic stiffness and mass matrices for the non-symmetric cross-sections are precisely evaluated. In order to illustrate the accuracy of this formulation, the present finite element solutions of thin-walled sandwich beams with non-symmetric open, single- and double-cell sections are presented and compared with available results. Especially, the effects of various structural parameters of thin-walled FG sandwich beams such as gradient index, thickness ratios of ceramic in flanges and webs, and non-symmetricity of cross-section on the warping to torsion ratio of cross-section and the spatially coupled natural frequencies are parametrically investigated.

Study in dimension precision of micro straight thin wall with Ti-6Al-4V titanium alloy under mesoscale

Deflection problems are important causes of deterioration to the dimensional precision of machining micro thin-walled components. Under mesoscale, the deflection of the cutting tool and micro thin-walled workpiece model is established based on the Euler-Bernoulli cantilever beam theory. Then a novel average thickness prediction model of micro straight thin wall is set up considering the runout, cutting tool, and workpiece deflection. Afterwards, based on experimental data, the model is modified by introducing a scale factor K. This modified model has been calibrated and validated with Ti-6Al-4V titanium alloy, and it can provide very accurate prediction results for the micro straight thin wall at average thickness. In addition, the law of micro thin wall milling forces is also studied. In the end, the effect of different micro straight thin-walled stiffness on micro thin-walled dimensional accuracy is analyzed. The study found that for the thickness of micro straight thin walls, 100 μm is an inflection point to distinguish dimension precision between macroscale and mesoscale.

Equivalent dipole sources to estimate the influence of extracellular myocardial anisotropy in thin-walled cardiac forward models

The extracellular domain of the heart is anisotropic, which affects volume conduction and therefore body surface potentials. This paper tests the hypothesis that when wall thickness is sufficiently small (such as in the atria), the effect of extracellular anisotropy can be estimated by modifying local dipole current sources. A formula based on the Gabor–Nelson equivalent dipole and on the reciprocity theorem is derived to compute a linear transformation of the dipole sources that approximates in an isotropic volume conductor the far-field of the actual sources in an anisotropic volume conductor. It involves solving three Poisson equation (once for all). The results obtained in an atrial model embedded in a boundary-element torso model suggest that when wall thickness is < 3 mm, simulated P waves are weakly altered by extracellular anisotropy during sinus rhythm: an anisotropy ratio of 4:1 typically reduced the longitudinal component of the dipole sources by < 3%, increased the transverse component by < 5%, and increased the transmural component by ≈ 25% (which may be relevant in case of epicardial-endocardial dissociation). Due to uncertainty on experimental conductivity values, it is proposed that atrial extracellular anisotropy may be neglected when computing P waves.

Effect of hydraulic diameter and aspect ratio on single phase flow and heat transfer in a rectangular microchannel

The effect of aspect ratio and hydraulic diameter on single phase flow and heat transfer in a single microchannel was investigated numerically and the results are presented in this paper. Previously, many studies in literature investigating the effect of geometrical parameters reached contradictory conclusions leaving some phenomena unexplained. Additionally, most researchers studied the effect of channel geometry by varying the channel height for a constant channel width or varying the width for a constant height. This means that the hydraulic diameter and aspect ratio vary simultaneously, which makes it difficult to identify the relative importance of the aspect ratio and the hydraulic diameter. In the present study, the effect of hydraulic diameter was studied by varying the channel width and depth while keeping the aspect ratio constant. The range of hydraulic diameters was 0.1–1mm and the aspect ratio was fixed at 1. In the second set of simulations, the aspect ratio ranged from 0.39 to 10 while the hydraulic diameter was kept constant at 0.56mm. The simulations were performed using the CFD software package ANSYS Fluent 14.5. The geometry investigated in this study includes symmetrical cylindrical inlet and outlet plenums and a microchannel. The fluid entered and left the channel vertically from the top in a direction normal to the channel axis. The dimensions of the inlet/outlet plenums (diameter and height measured from the channel bottom surface) were kept constant while the width and depth of the channel were varied. The simulations were conducted for a range of Reynolds numbers (Re=100–2000) and water was used as the working fluid. A three dimensional thin wall model was used to avoid conjugate heat transfer effects. A constant heat-flux boundary condition was applied at the bottom and vertical side walls of the channel, while the upper wall was considered adiabatic. The friction factor was found to decrease slightly with aspect ratio up to AR≈2 after which it increased with increasing aspect ratio. The results demonstrated that the slope of the velocity profile at the channel wall changes significantly with aspect ratio for AR>2. The effect of the aspect ratio and hydraulic diameter on the dimensionless hydrodynamic entry length is not significant. Also, the aspect ratio does not affect the heat transfer coefficient while the dimensionless Nusselt number increases with increasing hydraulic diameter. The friction factor was found to increase with increasing hydraulic diameter.

THREE-DIMENSIONAL MODEL OF LEFT CHAMBERS OF THE HEART BASED ON ECHOCARDIOGRAPHY DATA: AN INSTRUMENT FOR DEVELOPMENT OF TRANSCATHETER VALVES

Aim. Comparative analysis of the acquired with EchoCG method parameters of the left chambers of the heart and of mitral valve in normal state and in restrictive type of failure with further building up three-dimensional models of these variants of the fibrous anulus geometry, and of the left atrium, left ventricle and its outgoing tract. Material and methods. The study was done using 3D transthoracal and transesophageal EchoCG on Philips iE33 (Philips Healthcare, USA) in 30 patients with unchanged mitral valve (n=15) and in ischemic mitral regurgitation (n=15). Spatial configuration of the anulus fibrosus was investigated, and mitral valve, spatial and volumetric parameters of the left atrium and left ventricle. Data was processed in SciLab 4.1.2 software and exported to CATIA 5 modelling system, where the acquired curves were combined to 2 solid thin-wall models, and after linking of the surfaces — to a hard-bodied model with required thickness of the walls. Results. All studied parameters revealed significant differences (p<0,001) in groups comparison. In restrictive type of insufficiency, sizes of fibrous anulus increase: intercomissural diameter by 22%, front-back — by 13%, perimeter — by 28%, surface — by 79%. End systolic and diastolic volumes of the LV increase more than 2 times, which is related with more prominent sphericity of the LV, than normally. Increase of LA more than 1,5 times also combines with its geometry change towards sphere. Three dimensional computer model of the left heart chambers changed as a result of ischemic mitral failure, is created. The model can be implemented in creation, analysis and prediction of medical devices for the position and/or realized as the full-sized mockups, test systems and phantoms for development and education. Conclusion . The investigation of mitral valve characteristics and of the left heart chambers by method of 3D transthoracal and transesophageal echocardiography makes it to obtain the baseline data necessary for creation of 3D computed models of the anatomic area normal and disordered. Such models can be implemented in the development of implanted devices constructions, preliminary tests of medical devices and in training.

A micro-macro description for pseudoelasticity of NiTi SMAs subjected to nonproportional deformations

A micro-macro constitutive model is developed and applied to the prediction of the pseudoelasticity (PE) of NiTi shape memory alloys (SMAs) subjected to nonproportional loadings. It is based on the work by Gall et al. and takes into account different elastic properties of the austenite and martensite. In the constitutive model for a single crystal, the activation of forward and inverse martensitic transformations and the volume fraction of each of the 24 martensite variants (MVs), and the interaction between the MVs are considered. The constitutive behavior of polycrystalline NiTi SMAs is obtained by assembling that of single crystals of different orientations with finite element method (FEM). The corresponding numerical algorithm and FEM model are developed, in which an additional step is adopted to get rid of the MVs that may irrationally be activated during transformation calculation, which directly reduces the dimension of the Jacobian and enables the convergence and stability of the numerical implement of the model, especially in the cases of complex multiaxial nonproportional deformation. A thin-walled cylindrical model is suggested for finite element analysis, in which the texture microstructure in the materials formed during the cold-drawn processes can be considered. It is shown that the MVs activated under tension are different from those under compression, and when subjected to shear deformation the MVs activated contain those appearing during tension, and more MVs activated may account for the larger slope in the shear stress-strain curve. The PE of NiTi SMAs subjected to uniaxial strain and nonproportional strain by some paths in ε−γ/3 plane is simulated, and the satisfactory agreement between the simulated and experimental results demonstrates the validity of the approach developed.

‘One-half order shear deformation theory’ as a new naming for the transverse, but not in-plane rotational, shear deformable structural models

Based on Hamilton’s principle and using method of hypotheses, governing equations for the existing typical thin-walled structure analysis models are first derived systematically in addition to those for the author’s alternative beam and plate theories with the deformation concept that the total deflection w can be assumed as the sum of the bending and shearing deflections wb and ws, and in addition formal expressions of shear forces for some beam and plate models are described on the basis of the equilibrium condition as a solid. Two specific static beam boundary value analyses are then carried out based on the alternative, Euler-Bernoulli and Timoshenko beam theories for which the respective calculated results turn out to differ. Through the discussions, it is shown that in the alternative beam and plate theories only the half categories of shear deformations, which involve also in-plane rotational shearing in addition to transverse shearing, can be expressed explicitly in terms of fundamental variables, in contrast to the traditional first-order shear deformation theories. Thus, it is proposed to call the alternative theory ‘one-half order shear deformation theory’ as a new naming for the moderately thick structural models with the superimposed total deflection concept as w=wb+ws.

Leveraging feature information for defeaturing sheet metal feature-based CAD part model

ABSTRACTComplex models prepared in CAD applications are often simplified before using them in downstream applications like CAE, shape matching, multi-resolution modeling, etc. In CAE, the thin-walled models are often abstracted to a midsurface for quicker analysis. Computation of the midsurface has been observed to be effective when the original model is defeatured to its gross shape.Defeaturing in this paper proposes a novel approach for computation such gross shape and it works in two phases. First, a proposed sheet metal feature-based classification scheme (taxonomy) is used to determine the suppressibility of the features. Second, a method based on the size of remnant portions of the feature volume is developed to determine the eligibility for suppression. Case studies are presented to demonstrate the efficacy of the proposed approach. It shows that even after substantial reduction in the number of faces the gross shape retains all the important features needed for computation of a well-connected mids...

Crack restriction mechanism of thin wall metal parts fabricated by laser direct deposition shaping

In order to restrict the generation and propagation of cracks in thin wall metal parts fabricated by laser direct deposition shaping method, using ‘element birth and death’ technique, a three-dimensional multitrack and multilayer thin wall model was developed, and the deposition process was simulated. Different scanning methods, including long edge parallel reciprocating scanning, short edge parallel reciprocating scanning and interlayer orthogonal parallel reciprocating scanning, were introduced. The effects of different substrate preheating temperatures were also researched. The von Mises equivalent stress and its X-, Y- and Z-directional principal stresses were analysed in detail. Under the same conditions used in the simulations, the deposition experiments were conducted, and the crack generation and restriction mechanism of thin wall metal parts were further discussed.

Automatic hierarchical mid-surface abstraction of thin-walled model based on rib decomposition

Model simplification is imperative in the process of computer aided design (CAD) and computer aided engineering (CAE) integration. Mid-surface abstraction is the most effective method to simplify the thin-walled models. Many previous research efforts have been focused on the mid-surface abstraction, including the model decomposition based methods, Medial Axis Transform (MAT) based methods and Chordal Axis Transform (CAT) based methods. However, complex thin-walled models cannot be handled well due to the fact that there are some problems including low geometrical precision, poor topological structure, etc., in the above resultant mid-surface models. Especially, these methods are hard to be reused to generate the mid-surface model efficiently. Therefore, a hierarchical semantic mid-surface abstraction method is proposed for the thin-walled model based on rib feature decomposition in this paper. Firstly, a new hierarchical semantic structure is defined and applied on both the thin-walled models and mid-surface models. After that, the model decomposition is conducted based on the identified rib features and the hierarchical semantic information is obtained at the same time. Then, the offset operation and discretization based methods are used to obtain the mid-surface patch for each sub region with different semantic structure respectively. Finally, the mid-surface model with hierarchical semantic information is generated by stitching all discrete patches. Moreover, the above model can be reused to facilitate the rapid mid-surface abstraction of the changed model based on its hierarchical semantic structure. Several examples are given to demonstrate the outperformance of the proposed method.

An alternative first-order shear deformation concept and its application to beam, plate and cylindrical shell models

A physical–mathematical interpretation of the alternative first-order shear deformation concept proposed by the author is first presented to get rid of an intuitive aspect of its basic premise that the total deflection w can be assumed as the sum of the bending and transverse shear deflections wb and ws. Then, on the basis of several beam and plate illustrative examples, the qualitative theoretical framework of the alternative concept is clarified by comparing with the traditional Timoshenko beam and Mindlin–Reissner plate theories. In addition, a new first-order shear deformation cylindrical shell theory is developed based on the alternative concept and Hamilton’s principle to obtain a frequency formula for in-plane vibrations of a thick ring. Finally, the physical–mathematical position of the present theory among the conventional thin-walled structure analysis models is deliberated. The result shows that the present theory is regarded as a refined mathematical generalization of the so-called corrected classical theory and it could lead to a reduction in the number of fundamental variables and governing equations in the modeling of the transverse shear deformable composite structures.

The finite element model research of the pre-twisted thin-walled beam

Based on the traditional mechanical model of thin-walled straight beam, the paper makes analysis and research on the pre-twisted thin-walled beam finite element numerical model. Firstly, based on the geometric deformation differential relationship, the Saint-Venant warping strain of pre-twisted thin-walled beam is deduced. According to the traditional thin-walled straight beam finite element mechanical model, the finite element stiffness matrix considering the Saint-Venant warping deformations is established. At the same time, the paper establishes the element stiffness matrix of the pre-twisted thin-walled beam based on the classic Vlasov Theory. Finally, by calculating the pre-twisted beam with elliptical section and I cross section and contrasting three-dimensional solid finite element using ANSYS, the comparison analysis results show that pre-twisted thin-walled beam element stiffness matrix has good accuracy.

Electromagnetic thin-wall model for simulations of plasma wall-touching kink and vertical modes

The understanding of plasma disruptions in tokamaks and predictions of their effects require realistic simulations of electric current excitation in three-dimensional vessel structures by the plasma touching the walls. As discovered at JET in 1996 (Litunovski JET Internal Report contract no. JQ5/11961, 1995; Noll et al., Proceedings of the 19th Symposium on Fusion Technology, Lisbon (ed. C. Varandas &amp; F. Serra), vol. 1, 1996, p. 751. Elsevier) the wall-touching kink modes are frequently excited during vertical displacement events and cause large sideways forces on the vacuum vessel which are difficult to withstand in large tokamaks. In disruptions, the sharing of electric current between the plasma and the wall plays an important role in plasma dynamics and determines the amplitude and localization of the sideways force (Riccardo et al., Nucl. Fusion, vol. 40, 2000, p. 1805; Riccardo &amp; Walker, Plasma Phys. Control. Fusion, vol. 42, 2000, p. 29; Zakharov, Phys. Plasmas, vol. 15, 2008, 062507; Riccardo et al., Nucl. Fusion, vol. 49, 2009, 055012; Bachmann et al., Fusion Engng Des., vol. 86, 2011, pp. 1915–1919). This paper describes a flat triangle representation of the electric circuits of a thin conducting wall of arbitrary three-dimensional geometry. Implemented into the shell simulation code (SHL) and the source sink current code (SSC), this model is suitable for modelling the electric currents excited in the wall inductively and through current sharing with the plasma.

Abstract 19579: An Experimental Evaluation of the Compliance Mismatch Effects for Four Stent-graft Devices and a Multi-layer Flow Modulator (MFM) Device for the Treatment of Abdominal Aortic Aneurysms

Purpose: To experimentally investigate the arterial wall/device compliance mismatch of four stent-graft devices and a multi-layer flow modulator within the supra- and infra-renal locations for the treatment of Abdominal Aortic Aneurysms (AAA). Methods: Five devices were tested under physiologically flow conditions within a flow simulator system comprising of a patient-specific thin-walled flexible AAA model with replicated intraluminal thrombus (ILT) supported by the spinal column. Arterial pressure/diameter measurements were monitored and recorded at the supra- and infra-renal regions and various hemodynamic indicators were obtained to assess the effects of compliance mismatch. Results: At the suprarenal region, all devices except the Excluder™, significantly decreased the compliance by 10 - 21% (p&lt;0.002) and increased the stiffness values by 5 - 21% (p&lt;0.001). At the infrarenal region, three devices (Endurant™ and Excluder™) significantly decreased the compliance by 13 - 26% (p&lt;0.001), while the other three devices (MFM™, Zenith™ and Fortron™) did not significantly change the aortic compliance (p&gt;0.057). There was a variation of 10.9 - 16.0 m/s in pulse wave velocities with an increase of 8 - 238% (p&lt;0.001) in the reflection coefficient for all devices. The Excluder™ and Endurant TM devices doubled the infrarenal unstented median elastic modulus value (p&lt;0.001). Conclusions: Commercially available endovascular devices lower the arterial wall compliance and increase the wall stiffness at the stent/arterial wall interface by varying amounts. The Excluder™ was found to be the most compliant in the surprarenal region, while the MFM™ device was the most compliant in the infrarenal region.

The influence of scanning methods on the cracking failure of thin-wall metal parts fabricated by laser direct deposition shaping

In order to improve the quality of thin-wall metal parts fabricated by laser direct deposition shaping method, using “element birth and death” technique, a three-dimensional multitrack and multilayer thin-wall model was developed. Different scanning methods, including long-edge parallel reciprocating scanning, short-edge parallel reciprocating scanning and inter-layer orthogonal parallel reciprocating scanning, were researched. The Von Mises equivalent stress, and its X-directional, Y-directional and Z-directional principal stresses were analyzed in detail. Under the same conditions used in the simulations, the deposition experiments were conducted, and the influence of different scanning methods on the cracking failure behavior of thin-wall metal parts was discussed.