Key Engineering Materials Vols. 452-453

Abstract: Damage-involved structural pounding during earthquakes has been recently intensively studied using different impact force models. The results of the previous studies indicate that the linear viscoelastic model is relatively simple yet accurate in modelling pounding-involved behaviour of structures during earthquakes. The only shortcoming of the model is a negative value of the pounding force occurring just before separation, which does not have any physical explanation. The aim of the present paper is to verify the effectiveness of the modified linear viscoelastic model, in which damping term (related to modelling of damage effects) is activated only during the approach period of collision therefore overcoming this disadvantage. The accuracy of the model is checked in a number of comparative analyses, including the comparison with the results of impact experiments and shaking table experiments on pounding between two steel towers. The results of the study indicate that the use of the modified linear viscoelastic model leads to very similar pounding-involved responses as in the case of the linear viscoelastic model.

Abstract: In this work is indicated how it could be possible to evaluate the limit stress of the thermo-elastic phase of deformation by thermo-analysing the surface of the specimen during a static traction test. Adding the temperature curve measured on a small area of the surface (the hottest) to the classic stress-strain curve, it is possible to evaluate a limit temperature T0 coincident with the beginning of the non linear trend of the curve. The corresponding stress value is coincident with the fatigue limit of the analyzed component. As an example, the results of traction tests performed on two notched specimens, where the change of linearity in the temperature curve during static traction test was evident, are reported.

Abstract: In China many long span stone arch bridges were built in the last 5 decades, most of these bridges were built with micro-aggregate concrete joint masonry. However, the mechanical properties of this kind masonry have been seldom studied. Based on 5 groups of specimens with C30 or C40 micro-aggregate concrete joints and dressed blocks, shear strength of the masonry is tested and analyzed, friction coefficients and empiric formulas of shear strength of the masonry are presented in this paper, design value of shear strength of the masonry is assessed and discussed.

Abstract: We show that the behavior of T700/M21s and T800/M21s composite panels are affected by the influence of strain rates together with local shear and crush punch or global flexural strengths of the structure. A deterministic continuous composite material model has been developed as a LS-DYNA user defined material model for unidirectional composites on the basis of the Matzenmiller model widely used for woven composites. Initiation and evolution up to saturation and fracture are implemented for various and coupled damage mechanisms including delamination. Quasi-static and dynamic characterization tests laminates have been carried out on balanced angle ply [±θ] and used for calibration of numerical values. Impact induced damage from experiment’s measures and numerical predictions are compared for T800/M21S aeronautical samples impacted at 15J.

Abstract: Aluminium foam represents a new class of materials characterized by a large variability due to its porous structure. A simple and easy-to-use indicator of foam inhomogeneities is represented by apparent density, but this parameter does not give indications about differences existing in structural stiffness. To overcome this limit, the variability of natural frequency has been considered in this work in the case of commercial closed-cell aluminium foam. Moreover, fatigue and fracture properties of aluminium foam are not well studied. In this work standard three-point bend specimens SE(B) have been used to determine critical Crack-Tip Opening Displacement. The pre-crack phase, consisting in the application of appropriate fatigue load, has been monitored through modal analysis. Experimental results confirm the possibility of using this technique also in the initial step of fatigue failure process to quantify the amount of fatigue damage induced by repeated loads.

Abstract: DIC (Digital Image Correlation) based methodology gives full field measure of the displacement using a well defined algorithm for matching the images of loaded and load free component, so that displacement in a plane can be evaluated for a certain number of grid reference points on the analysed surface. In this work, the authors present an application of DIC technique to analyse fatigue damage phenomena in two notched GFRC laminates under tensile load. Damage analysis based on optical DIC technique has been performed to detect the damaged areas on the specimen surface. The damage evolution and failure mechanism has been followed monitoring two parameters: the local hysteresis area of stress-strain cycles, the local stiffness variation.

Abstract: Numerical simulations related to polar effects in an infinite extended granular layer under shearing movement and constant vertical pressure are presented. The mechanical behavior of cohesionless granular soil is described within the framework of micro-polar (Cosserat) continuum and using an elasto-plastic constitutive relation. The influence of Cosserat rotations and couple stresses are taken into account using the mean grain size as characteristic length. Finite element method in Updated Lagrangian (UL) frame is used to consider large deformations during calculations. The numerical results demonstrate that for large shearing movement, the shear deformations within the granular layer are localized into a narrow zone. The FE-calculations indicate that the polar effects manifest by the appearance of noticeable grain rotations, high void ratios, pronounced volume changes within the localized shear zone.

Abstract: All spacecrafts in earth orbit are subject to hypervelocity impact by micro-meteoroids and space debris, which can in turn lead to significant damage and catastrophic failure of spacecraft. Porous volcano rock was adopted as one of micro-meteoroid material due to their similar physical and geometric features. Two-stage light gas gun experiments were carried out for a 6mm diameter volcano rock projectile impact on an Al-Whipple shield within the speed range from 1 km/s to 3 km/s. An ANSYS/LS-DYNA software was employed and justified by experimental results, in which a porous geometrical model was established for volcano rock projectile. The higher speed range was extended from 3 km/s to 10 km/s by numerical simulation. The results of experiments and numerical simulation indicated that major damage on rear wall of the Whipple shield impacted by volcano rock projectile is caused by the fragments of bumper of the shield, which is different from that of aluminum projectile. And 5.5km/s is the critical speed of a 6mm diameter volcano rock projectile impact on the Whipple shield investigated.

Abstract: An optimal condition of thermal stress cleaving was investigated by assuming the element-by-element temperature rise situation using finite element method. The obtained thermal stress cleaving condition is found to be optimal for the symmetrical cleaving of a rectangular plate.