Key Engineering Materials Vols. 385-387

Abstract: Where the self weight of the overall slab needs to be considered, the quantity of in-situ concrete required can be reduced by the introduction of polystyrene void forms supplied and fixed to the precast panel during manufacture. In this study, new I-slab system with polystyrene form and precast concrete deck is proposed to reduce the construction period and the self weight of the slab. This paper presents experimental works on the bending and shear of the I-slabs. Five specimens were tested. The main parameters of experiments were the hole diameter of polystyrene form and the thickness of slab. Structural performance of I-slab was evaluated on the basis of failure mode, load-displacement curve, and ultimate strengths. Based on the test results, the critical punching shear sections were changed as test variables, so the punching shear strengths were very different. Test results indicated that the developed I-slab were very effective to increase the strength because of self weight reduction.

Abstract: The effect of mechanical stress on Barkhausen noise from 45-permalloy plate is reported for as-rolled plate and plates which are annealed at various temperatures up to 1000 K. The data are compared with data of magnetic permeability, coercive force and Vickers hardness. The Barkhausen noise energy detected has been found to increase linearly with nominal stress. The larger the annealing temperature, the less the rate of increase was observed. On the other hand, the magnetic permeability has been found to decrease linearly with nominal stress in a small stress region. Overall features are explained qualitatively by a model in which tensile stress makes the number of effective pinning sites which have appropriate activation energies for discontinuous motion of domain wall more, while annealing process makes just the number of pinning sites such as defects and grain boundaries less.

Abstract: In this paper, the deformation fields of LY12 crack samples loaded by an SHTB are real-time investigated with the time interval of 10 µs by an optical system, which consists of a high-speed camera, a flash light, a frame grabber and a synchronization device with the delay-time less than microsecond. The cracks are preset by using the three-points bending method in a MTS fatigue machine. The crack is 2mm long with a flare angle of 60 degree. During the experiments, the dynamic deformation images are captured by the high speed camera and analyzed by newly developed software based on Digital Correlation theory. And the displacements fields near crack-tips according to the changes of the flare angle and radius during the impact process are obtained. Experimental results acquired in this paper are proofed, by compared with the theoretical calculations.

Abstract: The high stress concentration at the edge of a non-circular shaped cutout is of practical importance in designing of the engineering structures. These types of cutout usually are evaluated either experimentally or numerically. In this paper an attempt is made to formulate a simple analytical method for stress analysis in perforated composite plates with non-circular cutouts. The stress concentration of isotropic and composite perforated plates with variety of centrally located non-circular cutout was investigated. Numerical evaluation using commercial finite element code, were conducted to evaluate the analytical results. Parametric studies were conducted to investigate the effects of variation in cutout shape, bluntness, and material properties on the location and the value of the maximum stress in plates subjected to uni-axial tension load. The results presented herein, indicated that the maximum stress in perforated isotropic/composite plates can be significantly change by using proper material properties, cutout shapes and bluntness.

Abstract: The fatigue life of metallic materials is strongly influenced by crack closure effects. Finite element (FE) methods allow the study of crack closure with great detail and can provide valuable information about phenomena occurring in the bulk of the material. In this work the distribution of stresses through the thickness of a cracked specimen has been studied using 3D FE simulations. It was found that the transition between the interior of the specimen (plane strain) and the surface (plane stress) differs from that predicted by 2D plane stress models. In addition, an attempt is presented to experimentally validate the results at the surface level. For this purpose full-field image correlation technique was utilized. This allowed direct comparison between the displacement field predicted by the numerical simulations and the experimental results measured by digital image correlation.

Abstract: Structures may enter into nonlinear stage under strong earthquake, so precise prediction of nonlinear behavior for building structure in earthquake is important which can assess the earthquake resistance safety of structures accurately. The exact numerical analysis model is required in actual engineering. In this paper the concept of nonlinear dynamic damage is introduced in steel reinforced concrete (SRC) composite structure, based on the theory of continuous damage mechanics. The damage variable is defined and computed by effective plastic strain of material, furthermore, concrete dynamic constitutive model is derived which considered plastic strain of material. Finally, the damage dynamic balance equation is established. Via comparison with test results of a three-story, two-bay SRC frame model which is tested on a shaking table, it is shown that the results of numerical analysis agree well with test results, indicating that the nonlinear dynamic balance equation is capable of describing the dynamic response of SRC frame structure with satisfactory accuracy. The research supplies theoretical basis for the seismic behavior analysis of SRC high-rise buildings.

Abstract: Performance level and life span of existing structural elements can be increased by repair and strengthening of these structural elements using advanced composite materials.The performance of damaged metallic plates reinforced with fiber-reinforced polymer composite materials (composite patch) are presented in this study. A square aluminum plate with a central circular cutout is considered as a damaged structural element. Numerical studies using commercial finite element code were conducted to investigate the effects of variation in patch geometries and lamination parameters on buckling responses of repaired plates. The varying laminate parameters such as, fiber angles and stacking sequences are considered in this study. A quantitative measure for the effectiveness of the composite patches is taken to be the relative change in buckling loads of the reinforced plates compare to those of the perfect one. The results presented herein indicated that, for buckling response of a repaired metallic plate with central cutout, a set of laminated composite patches with different shape and stacking sequences can be found which improve load carrying capacity of damaged plates.

Abstract: With the increase in the use of recycled aggregate concrete (RAC), it is necessary to clearly understand its behavior and characteristics. In this paper, experimental study on compressive strength of RAC with same water/cement ratio is conducted. Firstly, influence of recycled coarse aggregate contents on cube compressive strength of RAC is studied. Secondly, experiment on time-dependent strength developing process of RAC is conducted with different solidification ages. Finally, based on above experimental investigations, empirical formula for compress strengths of RAC with different ages is presented. The result of this paper is helpful to theoretical analysis and practical engineering design of RAC structures.

Abstract: The microbiological influenced corrosion (MIC) behavior of a marine pipeline Cu-Ni alloy in the sterile seawater and sulfate-reducing bacteria (SRB) solution was investigated. Results show that severe pitting corrosion appeared on the specimens in the SRB solution. The corrosion potential of specimen in the SRB solution was much lower than that in the sterile seawater and the polarization resistance of specimen in the SRB solution decreased quickly after a period immersion and became much lower than that in the sterile seawater. Besides, the results of EDS and XRD show that the content of element Ni and Fe of the Cu-Ni alloy decreased greatly and the high content of element S appeared after 30 days immersion in the SRB solution. It was concluded that the SRB accelerated the corrosion process of the Cu-Ni alloy greatly. The MIC mechanism of the alloy in marine environment is discussed.

Abstract: Dynamic interaction is investigated theoretically between a circular cavity and a crack near the surface in a semi-infinite piezoelectric medium subjected to time-harmonic incident anti-plane shearing in this paper. The formulations are based on the method of complex variable and Green’s function. Dynamic stress concentration factors at the edge of the circular cavity and dynamic stress intensity factors at the crack tip are obtained by solving boundary value problems with the method of orthogonal function expansion. The calculating results are plotted to show how the frequencies and the orientation of incident wave, piezoelectric characteristic parameters of the material and the structural geometries influence upon the dynamic stress concentration factor (DSCF) and dynamic stress intensity factor (DSIF).