Microstructural evolution and solidification cracking susceptibility of Fe–18Mn–0.6C–xAl steel welds

In this work, the solidification behavior and solidification cracking of Fe–18Mn–0.6C–xAl (x = 1.49, 2.37, 4.79, 6.04 wt%) alloys were investigated. A longitudinal Varestraint test was applied to evaluate the solidification cracking tendency of Al-added high-Mn steel welds. In terms of total crack length and maximum crack length at 4 % applied strain, the solidification cracking susceptibility of high-Mn steel decreased with increasing Al content. Addition of Al suppressed the formation of low melting point eutectics (γ + (Fe,Mn)₃C) along the grain boundaries during the final stage of solidification, which resulted in the decrease of solidification cracking tendency. The Al segregated extensively to the dendrite core opposite to Mn and C during solidification, which promoted the formation of δ ferrite. Further, the transition of the solidification sequence from the primary austenitic to primary ferritic mode provided a noticeable improvement in solidification cracking resistance in high-Mn steel welds similar to austenitic stainless steel welds.     

Efficient laminated composite beam element subjected to variable axial force for coupled stability analysis

A numerically efficient laminated composite beam element subjected to a variable axial force is presented for a coupled stability analysis. The analytical technique is used to present the thin-walled laminated composite beam theory considering the transverse shear and the restrained warping-induced shear deformation based on an orthogonal Cartesian coordinate system. The elastic strain energy and the potential energy due to the variable axial force are introduced. The equilibrium equations are derived from the energy principle, and explicit expressions for the displacement parameters are presented using the power series expansions of displacement components. Finally, the member stiffness matrix is determined using the force–displacement relations. In order to verify accuracy and efficiency of the beam element developed in this study, numerical results are presented and compared with results from other researchers and the finite beam element results, and the detailed finite shell element analysis results using ABAQUS; especially, the influence of variable axial forces, the fiber orientation, and boundary conditions on the buckling behavior of the laminated composite beams is parametrically investigated.     

Buckling and postbuckling of circular plates containing concentric penny-shaped delaminations

Buckling and postbuckling analyses of circular laminated composite plates with delaminations are presented. An axisymmetric finite element model based on a layer-wise laminated composite plate theory is developed to formulate the problem. Geometric nonlinearity in the sense of von Kármán and imperfections in the form of initial global deflection and initial delamination openings are included. A simple contact algorithm which precludes the physically inadmissible overlapping between delaminated surfaces is proposed and incorporated into the analysis.

Numerical results are obtained addressing the effects of the initial imperfections, the number of delaminations and their sizes on the critical buckling load and buckling mode shapes as well as postbuckling responses.     

Thermally induced buckling of laminated composites by a layerwise theory

Thermal buckling analysis of laminated composites is presented by using a layer-wise theory. Governing buckling equations are derived from the variational principle and a finite element method is developed to formulate the problem. Numerical results are obtained and compared with those of other theories addressing the effects of the thickness-to-span ratio, lamination angle, the ratio of thermal expansion coefficients and degree of orthotropy on buckling temperature for antisymmetric angle-ply laminates. It is found that a layer-wise approach may be necessary for more accurate thermal buckling analysis of laminated composites.     

Vibration analysis of thin-walled composite beams with I-shaped cross-sections

A general analytical model applicable to the vibration analysis of thin-walled composite I-beams with arbitrary lay-ups is developed. Based on the classical lamination theory, this model has been applied to the investigation of load–frequency interaction curves of thin-walled composite beams under various loads. The governing differential equations are derived from the Hamilton’s principle. A finite element model with seven degrees of freedoms per node is developed to solve the problem. Numerical results are obtained for thin-walled composite I-beams under uniformly distributed load, combined axial force and bending loads. The effects of fiber orientation, location of applied load, and types of loads on the natural frequencies and load–frequency interaction curves as well as vibration mode shapes are parametrically studied.     

Best Combination of Binarization Methods for License Plate Character Segmentation

A connected component analysis from a binary image is a popular character segmentation method but occasionally fails to segment the characters owing to image noise and uneven illumination. A multimethod binarization scheme that incorporates two or more binary images is a novel solution, but selection of binarization methods has never been analyzed before. This paper reveals the best combination of binarization methods and parameters and presents an in‐depth analysis of the multimethod binarization scheme for better character segmentation. We carry out an extensive quantitative evaluation, which shows a significant improvement over conventional single‐method binarization methods. Experiment results of six binarization methods and their combinations with different test images are presented.     

Flexural–torsional coupled vibration and buckling of thin-walled open section composite beams using shear-deformable beam theory

A general analytical model based on shear-deformable beam theory has been developed to study the flexural–torsional coupled vibration and buckling of thin-walled open section composite beams with arbitrary lay-ups. This model accounts for all the structural coupling coming from the material anisotropy. The seven governing differential equations for coupled flexural–torsional–shearing vibration are derived from Hamilton's principle. The resulting coupling is referred to as sixfold coupled vibration. Numerical results are obtained to investigate effects of shear deformation, fiber orientation and axial force on the natural frequencies, corresponding mode shapes as well as load–frequency interaction curves.     

Experimental study of RC beam–column joints strengthened using CFRP composites

This paper presents an experimental study to strengthen the shear capacity of non-seismic joints using Carbon Fiber Reinforced Plastic (CFRP) materials. Eight exterior RC beam–column joint specimens including a non-seismic specimen, a seismic specimen and six retrofitted specimens with different configurations of CFRP sheets were developed and tested to find out an effective way to improve the seismic performance of the joints in terms of the lateral strength and ductility. The different configurations of CFRP sheets considered were the T-shape, L-shape, X-shape and strip combinations. The research focused on the effect of using CFRP sheets for enhancing strength and increasing ductility of the non-seismic beam–column joints. The test results showed that appropriately adding CFRP composites to the non-seismic specimen significantly improved the lateral strength as well ductility of the test specimens. Especially, the X-shaped configuration of wrapping, the strips on the column and two layers of the CFRP sheets resulted in a better performance in terms of ductility and strength.     

On the approximation of fault directions for mutual detectability: an invariant zero approach

This note is concerned with the approximation of fault directions in relation to mutual detectability in detection filter problems. As an efficient system representation for analysis of detection order, we utilize the observer canonical form, by which we show that the invariant zero and the detection order can be analytically calculated by a set of polynomials associated with fault directions. Noting that this approach clearly shows the condition for the detection order to be plural, we propose a fault direction approximation method, which increases its detection order, for obtaining a mutually detectable system. Regarding the resulting degradation of fault isolation performance as a disturbance, we present its quantitative analysis and propose a method of selecting a threshold in order to guarantee proper fault isolation.