Key Engineering Materials Vols. 417-418

Abstract: Static loading and impact tests of ceramic alumina tiles have shown a very interesting behaviour of tough, brittle, and high energy absorbing materials. Strain gauges techniques and data acquisition were used in previous research for static and low velocity impact testing. A static-dynamic equivalence was done through a calibration procedure of the measuring system. The research is continued in this paper by using the digital image correlation method with the complete displacement and strain history acquired till the failure of the ceramic tiles of different compositions, proving the capacity of such materials to be used for particular purpose applications.

Abstract: The influence of concrete meso-structure and coarse aggregate size on early age crack is studied. In this study, concrete is regarded as a three-phase material based on shrinkage property. The mortar matrix and interfacial transition zones undergo shrinkage and no spherical coarse aggregate particles are considered to restain the shrinkage by particle interaction. The results show that concrete meso-structure plays an important role in the safety of concrete, different aggregate distribution in concrete leads to different initial cracks and propagation due to shrinkage. With the increase of maximum aggregate size, the value of shrinkage deformation becomes unstable and varies in a wide range; relevant shrinkage cracking becomes easier too.

Abstract: Fracture analysis has been made for a 2 dimensional prototype of recycled aggregate concrete using the discrete cracking model. The discrete element method has been developed based on quasi-brittle constitutive law to simulate the behavior of the 2 dimensional recycled aggregate concrete prototype under uniaxial compressive loading. The relationship between stress distribution and failure mechanism of the recycled aggregate concrete plate has been investigated and analyzed. The numerical model proposed in the paper is in the first time used to analyze the mechanical properties of recycled aggregate concrete. Efficiency and accuracy of the numerical model has been demonstrated. It is indicated that this model has potential to be extended for 3 dimensional structural analysis of recycled aggregate concrete.

Abstract: The energy absorption capability of an exposed crashworthy element or system is largely affected by material properties and structural design: prismatic sandwich structures, made of foam or honeycomb core between two metallic or laminated composite face plates, are good candidates. This work deals with a numerical investigation on the energy absorbing capability of such a structural component. There are several difficulties associated with the numerical simulation of a composite impact-absorber, such as high geometrical non-linearities, boundary contact conditions, failure criteria, material behaviour; that is because the main objectives of any numerical investigation are the calibration of the model with experimental results and the evaluation of the sensitivity of the variables with respect to the geometrical and physical parameters which influence the study at hand. The latter is a very relevant aspect for designers if the application of the model to real cases has to be a robust one from both a physical and a numerical point of view. In this paper a preliminary calibration of a numerical model for a composite impact absorber is presented, on the basis of experimental data found in literature; then a sensitivity analysis of the same model to the variation of the main geometrical and material parameters, developed by using the explicit finite element algorithms implemented in the Ls-Dyna code, is illustrated.

Abstract: A random aggregate model of recycled aggregate concrete is developed in this paper on the base of a mixture ratio. Combining a lattice model with random aggregate of recycled aggregate concrete, lattice elements in the lattice model of recycled aggregate concrete can be classified into five types: (1) nature aggregate, (2) old hardened mortar, (3) new hardened mortar, (4) old interface transition zone (ITZ), and (5) new ITZ. The fundamental mechanical parameters of the lattice elements are chosen from the authors’ test as well as other references. A FORTRAN program of the lattice model is then written with basic theories of finite element method (FEM) for simulating the meso-structural damage of recycled aggregate concrete under uniaxial compression.

Abstract: At the stress-strain tests for the overhead electrical conductors stranded in alternate directions (aluminum conductor steel reinforced - ACSR), the locking mode of the specimen ends on the tensile machine represents a difficult problem which if is not correctly solved may seriously influence the results obtained. The stress-strain tests are performed according to standards as the European Standard EN 50182:2001. The specimen must have a length imposed by the conductor diameter, but not less than 10m. During the stress-strain tests the specimen is loaded in steps at successive cycles of loading- unloading (30%, 50%, 70%, 85% of Rated Tensile Stress –RTS). Finally, in order to determine the breaking forces, the conductor is loaded up to total breaking. In these conditions, the test success is decisively influenced by the correct locking of the conductor in the grips. The locking of the conductor ends is usually performed by casting the conductor ends in the gripping devices, after the wires ends reflection. In this paper there is presented a new locking method of the conductor ends by separation of the steel wires from the aluminum ones and their separate winding on two drums with helical groove. The tests performed have confirmed that this method is cheaper, and not influencing the real behavior of the conductor.

Abstract: Concrete exposing to atmosphere suffers from changes in its internal structure, for instance loss of alkalinity of the cover concrete and corrosion of steel rebar due to carbonation, which in extreme cases affect the safety, the reliability and the durability or the service life of the structure. Carbonation is one of the key environmental actions that may cause structural failure. This study aims to gain some new information on the carbonation resistance when recycled coarse aggregates are used to mix new concrete. The concrete’s resistance to carbonation is determined by measuring the carbonation depth of 100mm×100mm×300mm concrete prisms in according to GBJ 82-85. Two series of tests including 9 groups of recycled aggregate concrete specimens are carried out, in which the effects of the quality and replacement of recycled coarse aggregates on the carbonation behavior of recycled concrete are evaluated. The essential test results are presented and discussed in this paper. Based on the findings of the present study, in order to reduce the unfavorable effects of recycled coarse aggregates on the recycled concrete, limiting the compressive strength grade of original concrete and the replacement of recycled coarse aggregate is a good option under the condition of using recycled concrete in considered projects.

Abstract: The performance of perforated metallic plates repaired with laminated composite patches is 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 laminate parameters such as number of plies, fiber orientation, and stacking sequences on free vibration responses of the repaired plates. Particular emphasis is placed on the effect of imperfect bonding (patch debonding). A quantitative measure for the effectiveness of the composite patches parameters is taken to be the relative change in natural frequencies of the deboned patches compare to the patches with perfect bonding. The results presented herein indicated that, vibration response of a repaired perforated metallic plate is affected by the number of plies, stacking sequences of the patch and the quality of bonding between the patch and the base plate.

Abstract: The deficiency of present damage model is generalized by studying existing references. The mechanical properties of steel reinforced high strength and high performance concrete (SRHSHPC) members under monotonic loading, including the capacity of ultimate deformation, strength, stiffness, etc. are analyzed after the different number of cycles. The reduction factor is introduced, the dynamic variation relationship of ultimate deformation with the number of cycles is obtained, and the merits of existing damage model are utilized, finally the seismic damage model, which is suitable for SRHSHPC beam-column joints, is established. In order to verify the rationality of damage model, Opensees as a nonlinear analysis program is adopted to simulate SRHSHPC joints, the comparison of the numerical analysis results with experimental results shows that the proposed damage model can capture the behaviors of joints very well. The model can, therefore, be used to carry out seismic damage analysis of other SRHSHPC members.

Abstract: This study investigates the application of laminated composite patches for enhancement of flutter behavior of perforated metallic plates repaired with an external composite patch. Due to material anisotropy and discontinuity in geometry involved in flutter analysis of repaired plates, closed form solutions are practically unobtainable. Numerical studies using commercial finite element software were conducted to investigate the effects of variation in lamination parameters on the flutter boundary of perforated plates repaired with cross-ply composite patches. Both ply-level and sub-laminate level configurations are investigated. Presented results illustrate that flutter boundaries of perforated plates can be changed by choosing proper stacking sequence for composite patches.