Smooth Strains Research Articles

Stabilized and variationally consistent nodal integration for meshfree modeling of impact problems

Galerkin meshfree methods can suffer from instability and suboptimal convergence if the issue of quadrature is not properly addressed. The instability due to quadrature is further magnified in high strain rate events when nodal integration is used. In this paper, several stable and convergent nodal integration methods are presented and applied to transient and large deformation impact problems, and an eigenvalue analysis of the methods is also provided. Optimal convergence is attained using variationally consistent integration, and stability is achieved by employing strain smoothing and strain energy stabilization. The proposed integration methods show superior performance over standard nodal integration in the wave propagation and Taylor bar impact problems tested.

A cell-based smoothed three-node Mindlin plate element (CS-FEM-MIN3) based on the C0-type higher-order shear deformation for geometrically nonlinear analysis of laminated composite plates

A cell-based smoothed three-node Mindlin plate element (CS-FEM-MIN3) based on the first-order shear deformation theory (FSDT) was recently proposed for static and free vibration analyses of Mindlin plates. In this paper, the CS-FEM-MIN3 is extended to geometrically nonlinear analysis of laminated composite plates. The nonlinear formulation is based on the C0-type high-order shear deformation plate theory (C0-HSDT) and the von Kármán strains, which deal with small strains and moderate rotations. In the process of formulating the system stiffness matrix of the CS-FEM-MIN3, each triangular element will be divided into three sub-triangles, and in each sub-triangle, the MIN3 is used to compute the strains. Then the strain smoothing technique on whole the triangular element is used to smooth the strains on these three sub-triangles. The accuracy and reliability of the proposed method is verified by comparing its numerical solutions with those of available other numerical results.

A locking‐free selective smoothed finite element method using tetrahedral and triangular elements with adaptive mesh rezoning for large deformation problems

SUMMARYA novel finite element (FE) formulation with adaptive mesh rezoning for large deformation problems is proposed. The proposed method takes the advantage of the selective smoothed FE method (S‐FEM), which has been recently developed as a locking‐free FE formulation with strain smoothing technique. We adopt the selective face‐based smoothed/node‐based smoothed FEM (FS/NS‐FEM‐T4) and edge‐based smoothed/node‐based smoothed FEM (ES/NS‐FEM‐T3) basically but modify them partly so that our method can handle any kind of material constitutive models other than elastic models. We also present an adaptive mesh rezoning method specialized for our S‐FEM formulation with material constitutive models in total form. Because of the modification of the selective S‐FEMs and specialization of adaptive mesh rezoning, our method is locking‐free for severely large deformation problems even with the use of tetrahedral and triangular meshes. The formulation details for static implicit analysis and several examples of analysis of the proposed method are presented in this paper to demonstrate its efficiency. Copyright © 2014 John Wiley & Sons, Ltd.

Development of a strain-smoothed three-node triangular flat shell element with drilling degrees of freedom

This paper proposes a three-node triangular flat shell element based on the assumed natural deviatoric strain (ANDES) formulation. The free parameters included in the ANDES formulation are presented for better use of the proposed element in curved shell geometries. In order to further enhance the element behavior, a strain smoothing technique is applied to the derivation of the membrane stiffness of the proposed element. Furthermore, in order to avoid the drill rotation locking that is typically induced by the drilling degrees of freedom, a simple modification factor is introduced. Various benchmark examples are tested in order to verify the performance of the proposed element.

An edge-based smoothed three-node mindlin plate element (ES-MIN3) for static and free vibration analyses of plates

The edge-based strain smoothing technique is combined with the three-node Mindlin plate element (MIN3) to give a so-called the edge-based smoothed three-node Mindlin plate element (ES-MIN3) for static and free vibration analyses of plates. In the formulation of the ES-MIN3, the MIN3 together with a shear stabilized technique is used to compute the strains and to avoid the shear locking. Then the strain smoothing technique on the smoothing domains associated with edges of elements is used to smooth the strains on the adjacent elements. This strain smoothing technique can provide proper softening effect, which will effectively relieve the stiff behavior of the MIN3 and thus improve significantly the accuracy of solutions. The numerical examples demonstrated that the ESMIN3 is free of shear locking, passes the patch test and shows three superior properties such as: (1) be a strong competitor to others existing plate elements in the static analysis; (2) can give high accurate solutions in free vibration analysis; (3) can provide accurately the values of high frequencies of plates by using only coarse meshes.

Convergence and accuracy of displacement based finite element formulations over arbitrary polygons: Laplace interpolants, strain smoothing and scaled boundary polygon formulation

Three different displacement based finite element formulations over arbitrary polygons are studied in this paper. The formulations considered are the conventional polygonal finite element method (FEM) with Laplace interpolants, the cell-based smoothed polygonal FEM with simple averaging technique and the scaled boundary polygon formulation. For the purpose of numerical integration, we employ the sub-triangulation for polygonal FEM and classical Gaussian quadrature for the smoothed FEM and the scaled boundary polygon formulation. The accuracy and the convergence properties of these formulations are studied with a few benchmark problems in the context of linear elasticity and the linear elastic fracture mechanics. The extension of scaled boundary polygon to higher order polygons is also discussed.

Towards a receptor-free immobilization and SERS detection of urinary tract infections causative pathogens

Based on molecular-specific surface-enhanced Raman scattering (SERS) spectroscopy we were able to discriminate between rough and smooth strains of Escherichia coli and Proteus mirabilis bacteria. For this purpose, bacteria have been immobilized through electrostatic forces by inducing a positive charge on the glass slide. This way, SERS spectra on bacterial biomass and also on single bacteria could be recorded in less than 2 h, by using concentrated silver nanoparticles as SERS-active substrate. Single-bacterium SERS spectral fingerprints showed to be sensitive to the presence of the O-antigen at strain level and to the microorganisms growth phase. By using principal component analysis (PCA) on the SERS spectra recorded from E. coli and P. mirabilis, these two uropathogens could be fairly discriminated.

The verification of the quantities of interest based on energy norm of solutions by node-based smoothed finite element method

Verification of the quantities of interest computed with the finite element method (FEM) requires an upper bound on the strain energy, which is half of the energy norm of displacement solutions. Recently, a modified finite element method with strain smoothing, the node-based smoothed finite element method (NS-FEM), has been proposed to solve solid mechanics problems. It has been found in some cases that the energy norm formed by the smoothed strain of NS-FEM solutions bounds the energy norm of exact displacements from above. We analyze the bounding property of this method, give three kind of energy norms of solutions computed by FEM and NS-FEM, and extend them to the computation of an upper bound and a lower bound on the linear functional of displacements. By examining the bounding property of NS-FEM with different energy norms using some linear elastic problems, the advantages of NS-FEM over the traditional error estimate based methods is observed.

A sub‒domain smoothed Galerkin method for solid mechanics problems

SUMMARYA sub‒domain smoothed Galerkin method is proposed to integrate the advantages of mesh‒free Galerkin method and FEM. Arbitrarily shaped sub‒domains are predefined in problems domain with mesh‒free nodes. In each sub‒domain, based on mesh‒free Galerkin weak formulation, the local discrete equation can be obtained by using the moving Kriging interpolation, which is similar to the discretization of the high‒order finite elements. Strain smoothing technique is subsequently applied to the nodal integration of sub‒domain by dividing the sub‒domain into several smoothing cells. Moreover, condensation of DOF can also be introduced into the local discrete equations to improve the computational efficiency. The global governing equations of present method are obtained on the basis of the scheme of FEM by assembling all local discrete equations of the sub‒domains. The mesh‒free properties of Galerkin method are retained in each sub‒domain. Several 2D elastic problems have been solved on the basis of this newly proposed method to validate its computational performance. These numerical examples proved that the newly proposed sub‒domain smoothed Galerkin method is a robust technique to solve solid mechanics problems based on its characteristics of high computational efficiency, good accuracy, and convergence. Copyright © 2014 John Wiley & Sons, Ltd.

Validation of a simple universal IELISA for the diagnosis of human brucellosis

The definitive diagnosis of brucellosis requires isolation of the agent, although negative isolation does not rule out the infection. In contrast, serological testing is more sensitive and, therefore, preferred in clinical practice. The majority of reported cases around the world were caused by Brucella melitensis, B. abortus, B. suis and B. canis. The first three species contain O-polysaccharide (OPS) on the cell surface, but B. canis contains no measurable OPS on the rough lipopolysaccharide (R-LPS). A universal indirect enzyme immunoassay for the detection of serum antibody to smooth and rough Brucella spp. in both normal (u-IELISA®) and rapid forms (R-u-IELISA®) has been developed, and, therefore, the potential use of this method was assessed in comparison to cELISA, conventional tests, IELISA and RSAT on a total of 478 sera. The 77 sera from blood donors with no clinical or epidemiological evidence of brucellosis and negative serological tests showed a specificity of 100 % for both u-IELISA® and R-u-IELISA®, with a cut-off value of %P 24 and %P 18, respectively. Sera from 49 culture-positive cases (16 B. suis, 15 B. abortus, 12 B. melitensis and 6 B. canis) yielded a sensitivity of 98 % for u-IELISA® and 95.9 % for R-u-IELISA®. In general, u-IELISA® showed good correlation with cELISA and IELISA for the detection of antibodies to smooth and rough Brucella strains, as well as for monitoring patients during treatment, but R-u-IELISA® seems to need additional optimisation. u-IELISA® is simple to perform and could be a suitable test for field laboratories and hospitals lacking skilled personnel.

Evaluation of the immunogenicity and safety of Brucella melitensis B115 vaccination in pregnant sheep

In spite of its limitations, Rev.1 is currently recognized as the most suitable vaccine against Brucella melitensis (the causative agent of ovine and caprine brucellosis). However, its use is limited to young animals when test-and-slaughter programs are in place because of the occurrence of false positive-reactions due to Rev.1 vaccination. The B. melitensis B115 rough strain has demonstrated its efficacy against B. melitensis virulent strains in the mouse model, but there is a lack of information regarding its potential use in small ruminants for brucellosis control. Here, the safety and immune response elicited by B115 strain inoculation were evaluated in pregnant ewes vaccinated at their midpregnancy. Vaccinated (n=8) and non-vaccinated (n=3) sheep were periodically sampled and analyzed for the 108 days following inoculations using tests designed for the detection of the response elicited by the B115 strain and routine serological tests for brucellosis [Rose Bengal Test (RBT), Complement Fixation Test (CFT) and blocking ELISA (ELISAb)]. Five out of the 8 vaccinated animals aborted, indicating a significant abortifacient effect of B115 inoculation at midpregnancy. In addition, a smooth strain was recovered from one vaccinated animal, suggesting the occurrence of an in vivo reversion phenomenon. Only one animal was positive in both RBT and CFT simultaneously (91 days after vaccination) confirming the lack of induction of cross-reacting antibody responses interfering with routine brucellosis diagnostic tests in most B115-vaccinated animals.

A cell-based smoothed discrete shear gap method (CS-FEM-DSG3) using layerwise theory based on the C0-HSDT for analyses of composite plates

A cell-based smoothed discrete shear gap method (CS-FEM-DSG3) based on the first-order shear deformation theory (FSDT) using triangular element was recently proposed for static and dynamics analyses of Mindlin plates. In this paper, the CS-FEM-DSG3 is extended and incorporated with a layerwise theory for static and free vibration analyses of composite and sandwich plates. In the layerwise theory, the behavior of each layer follows the C0-type higher-order shear deformation theory (C0-HSDT) and the condition of displacement continuity is imposed at the interfaces of layers. The shear correction factor is hence no more necessary and the accuracy of transverse shear stresses is improved significantly. In the process of formulating the system stiffness matrix of the CS-FEM-DSG3, each triangular element will be divided into three sub-triangles, and in each sub-triangle, the stabilized discrete shear gap method (DSG3) is used to compute the strains. Then the strain smoothing technique on whole the triangular element is used to smooth the strains on these three sub-triangles. Some numerical studies have been conducted to demonstrate the efficient performance of the proposed formulation.

Static and free vibration analyses of composite and sandwich plates by an edge-based smoothed discrete shear gap method (ES-DSG3) using triangular elements based on layerwise theory

An edge-based smoothed stabilized discrete shear gap method (ES-DSG3) based on the first-order shear deformation theory (FSDT) was recently proposed for static and dynamic analyses of Mindlin plates. In this paper, the ES-DSG3 is extended and incorporated with a layerwise theory for static and free vibration analyses of composite and sandwich plates. In the layerwise theory, the behavior of each layer follows the first-order shear deformation theory and the condition of displacement continuity is imposed at the interfaces of layers. This hence does not require shear correction factors and improves significantly the accuracy of transverse shear stresses. The stiffness formulation of the ES-DSG3 is performed by using the strain smoothing technique over the smoothing domains associated with edges of elements for each layer. The accuracy and reliability of the proposed method are confirmed in several numerical examples.

Characterization of Proinflammatory Responses and Innate Signaling Activation in Macrophages Infected with Mycobacterium scrofulaceum.

Mycobacterium scrofulaceum is an environmental and slow-growing atypical mycobacterium. Emerging evidence suggests that M. scrofulaceum infection is associated with cervical lymphadenitis in children and pulmonary or systemic infections in immunocompromised adults. However, the nature of host innate immune responses to M. scrofulaceum remains unclear. In this study, we examined the innate immune responses in murine bone marrow-derived macrophages (BMDMs) infected with different M. scrofulaceum strains including ATCC type strains and two clinically isolated strains (rough and smooth types). All three strains resulted in the production of proinflammatory cytokines in BMDMs mediated through toll-like receptor-2 and the adaptor MyD88. Activation of MAPKs (extracellular signal-regulated kinase 1/2, and p38, and c-Jun N-terminal kinase) and nuclear receptor (NF)-κB together with intracellular reactive oxygen species generation were required for the expression of proinflammatory cytokines in BMDMs. In addition, the rough morphotypes of M. scrofulaceum clinical strains induced higher levels of proinflammatory cytokines, MAPK and NF-κB activation, and ROS production than other strains. When mice were infected with different M. scrofulaceum strains, those infected with the rough strain showed the greatest hepatosplenomegaly, granulomatous lesions, and immune cell infiltration in the lungs. Notably, the bacterial load was higher in mice infected with rough colonies than in mice infected with ATCC or smooth strains. Collectively, these data indicate that rough M. scrofulaceum induces higher inflammatory responses and virulence than ATCC or smooth strains.

First Evidence for a Covalent Linkage between Enterobacterial Common Antigen and Lipopolysaccharide in Shigella sonnei Phase II ECALPS

Enterobacterial common antigen (ECA) is expressed by Gram-negative bacteria belonging to Enterobacteriaceae, including emerging drug-resistant pathogens such as Escherichia coli, Klebsiella pneumoniae, and Proteus spp. Recent studies have indicated the importance of ECA for cell envelope integrity, flagellum expression, and resistance of enteric bacteria to acetic acid and bile salts. ECA, a heteropolysaccharide built from the trisaccharide repeating unit, →3)-α-D-Fucp4NAc-(1→4)-β-D-ManpNAcA-(1→4)-α-D-GlcpNAc-(1→, occurs as a cyclic form (ECA(CYC)), a phosphatidylglycerol (PG)-linked form (ECA(PG)), and an endotoxin/lipopolysaccharide (LPS)-associated form (ECA(LPS)). Since the discovery of ECA in 1962, the structures of ECA(PG) and ECA(CYC) have been completely elucidated. However, no direct evidence has been presented to support a covalent linkage between ECA and LPS; only serological indications of co-association have been reported. This is paradoxical, given that ECA was first identified based on the capacity of immunogenic ECA(LPS) to elicit antibodies cross-reactive with enterobacteria. Using a simple isolation protocol supported by serological tracking of ECA epitopes and NMR spectroscopy and mass spectrometry, we have succeeded in the first detection, isolation, and complete structural analysis of poly- and oligosaccharides of Shigella sonnei phase II ECA(LPS). ECA(LPS) consists of the core oligosaccharide substituted with one to four repeating units of ECA at the position occupied by the O-antigen in the case of smooth S. sonnei phase I. These data represent the first structural evidence for the existence of ECA(LPS) in the half-century since it was first discovered and provide insights that could prove helpful in further structural analyses and screening of ECA(LPS) among Enterobacteriaceae species.

Characteristics of Saccharomyces cerevisiae yeasts exhibiting rough colonies and pseudohyphal morphology with respect to alcoholic fermentation

Among the native yeasts found in alcoholic fermentation, rough colonies associated with pseudohyphal morphology belonging to the species Saccharomyces cerevisiae are very common and undesirable during the process. The aim of this work was to perform morphological and physiological characterisations of S. cerevisiae strains that exhibited rough and smooth colonies in an attempt to identify alternatives that could contribute to the management of rough colony yeasts in alcoholic fermentation. Characterisation tests for invasiveness in Agar medium, killer activity, flocculation and fermentative capacity were performed on 22 strains (11 rough and 11 smooth colonies). The effects of acid treatment at different pH values on the growth of two strains (“52” - rough and “PE-02” - smooth) as well as batch fermentation tests with cell recycling and acid treatment of the cells were also evaluated. Invasiveness in YPD Agar medium occurred at low frequency; ten of eleven rough yeasts exhibited flocculation; none of the strains showed killer activity; and the rough strains presented lower and slower fermentative capacities compared to the smooth strains in a 48-h cycle in a batch system with sugar cane juice. The growth of the rough strain was severely affected by the acid treatment at pH values of 1.0 and 1.5; however, the growth of the smooth strain was not affected. The fermentative efficiency in mixed fermentation (smooth and rough strains in the same cell mass proportion) did not differ from the efficiency obtained with the smooth strain alone, most likely because the acid treatment was conducted at pH 1.5 in a batch cell-recycle test. A fermentative efficiency as low as 60% was observed with the rough colony alone.

Interlayer micromechanics of the aortic heart valve leaflet

While the mechanical behaviors of the fibrosa and ventricularis layers of the aortic valve (AV) leaflet are understood, little information exists on their mechanical interactions mediated by the GAG-rich central spongiosa layer. Parametric simulations of the interlayer interactions of the AV leaflets in flexure utilized a tri-layered finite element (FE) model of circumferentially oriented tissue sections to investigate inter-layer sliding hypothesized to occur. Simulation results indicated that the leaflet tissue functions as a tightly bonded structure when the spongiosa effective modulus was at least 25 % that of the fibrosa and ventricularis layers. Novel studies that directly measured transmural strain in flexure of AV leaflet tissue specimens validated these findings. Interestingly, a smooth transmural strain distribution indicated that the layers of the leaflet indeed act as a bonded unit, consistent with our previous observations (Stella and Sacks in J Biomech Eng 129:757-766, 2007) of a large number of transverse collagen fibers interconnecting the fibrosa and ventricularis layers. Additionally, when the tri-layered FE model was refined to match the transmural deformations, a layer-specific bimodular material model (resulting in four total moduli) accurately matched the transmural strain and moment-curvature relations simultaneously. Collectively, these results provide evidence, contrary to previous assumptions, that the valve layers function as a bonded structure in the low-strain flexure deformation mode. Most likely, this results directly from the transverse collagen fibers that bind the layers together to disable physical sliding and maintain layer residual stresses. Further, the spongiosa may function as a general dampening layer while the AV leaflets deforms as a homogenous structure despite its heterogeneous architecture.

An Efficient Technique for Surface Strain Recovery from Photogrammetric Data using Meshless Interpolation

ABSTRACTIn recent years, techniques for monitoring displacements and surface strains in laboratorial tests have been introduced. Some of those methods are based on photogrammetry and image post‐processing, allowing both displacement and strain fields to be monitored at a significant number of target points at any stage.This manuscript aims at contributing by proposing a simple and comprehensive approach for monitoring experimental tests using photogrammetry. An innovative strategy is introduced to efficiently recover the strain fields at the surface of a loaded specimen. This technique is based on a meshless approach and does not require any triangulation of data points. In this approach, shape functions are constructed from radial basis function interpolation in local subdomains, for which different numbers of data points may be included. To allow accounting for the presence of generic geometries, which may include concavities or convexities, the selection of interpolating points is performed considering a line‐of‐sight algorithm, avoiding inappropriate selection of neighbouring points.A number of practical examples are here presented for different concrete specimens tested in the laboratory. The presented results indicate that the proposed method can provide smooth strain fields, which allow an easy identification of microcracking development at early stages of loading.

Conductance across strain junctions in graphene nanoribbons

To address the robustness of the transport gap induced by locally strained regions in graphene nanostructures, the effect of disorder and smoothness of the interface region is investigated within the Landauer-B\"uttiker formalism. The electronic conductance across strained junctions and barriers in graphene nanoribbons is calculated numerically, with and without various types of disorder, and comparing smooth and sharp strain junctions. A smooth strain barrier in graphene is seen to be generically as efficient in suppressing transport at low densities as a sharp one, and the critical density (or energy) for the onset of transmission depends on the strain orientation with respect to the ribbon. In addition, hopping (or strain) inhomogeneity and work function mismatch at the interface region do not visibly degrade the transport gap. These results show that the strain-induced transport gap at a strain junction is robust to more realistic strain conditions.

A three-dimensional ES-FEM for fracture mechanics problems in elastic solids

The edge-based smoothed finite element method (ES-FEM) using triangular mesh was recently proposed to model the fracture problems in 2D solids. This paper contains the following ingredients: (1) the ES-FEM is extended to three-dimensional (3D) ES-FEM using tetrahedral elements to compute the stress intensity factors and simulate crack propagation in 3D elastic solids; (2) to model the singular fields of arbitrary order near the crack front, a layer of specially designed seven-noded crack-tip element is constructed; (3) the displacement is then enriched with ease to reproduce the necessary order of stress singularity; and (4) the enrichment is done without losing the essential properties of partition-of-unity and the linear function reproduction. Because the singular ES-FEM uses the strain smoothing technique and it is a typical weakened weak (W2) formulation, the system stiffness matrix is computed employing only the shape function values on the surface of the smoothing domains created based on the edges of elements. No derivatives of the shape functions are needed, and thus no mapping and integration for the W2 form is required. Several numerical examples are presented to validate the effectiveness of the proposed method.