Key Engineering Materials Vols. 348-349

Abstract: Aim of this paper is to study the impact between the sailing boat keel and the ground and to look for the optimal configuration of the bulb-keel-hull system able to direct the damage in the bulb-keel zone avoiding the hull region. The research, which is carried out in collaboration with Wally shipyard, requires firstly an accurate investigation of the bulb-keel-hull system geometry, of the boat inertial properties and of the impact condition. Secondly, a numerical dynamic analysis by means of the finite element method allows to model the impact and to determine how, during the collision, the state of stress varies and how the kinetic energy is absorbed/dissipated. Starting from these results, the performance of the present configuration is evaluated in several conditions and some proposals for new design configuration are made. In particular the results carried out from the new design analyses were evaluated comparing themselves to results obtained from experimental studies.

Abstract: The aim of this paper is to seek the solution to the electromechanical field equations for a cracked linear piezoelectric body using an analytical approach which is based on the decomposition theorem of linear algebra. The electroelastic fields around the crack tip are given. The energy release rate is written in terms of those fields intensity factors.

Abstract: Most of the previous studies utilized the maximum applied load and the initial crack length to determine the fracture criterion for Ⅰ-Ⅱ mixed mode fracture of concrete. Actually, the crack has propagated in the ultimate state due to the semi-brittle behaviors of concrete. Therefore, adopting the initial fracture toughness as the fracture criterion seems more reasonable. This subject carried out an experiment of four-point shearing notched beams of concrete with five different heights, i.e, 200mm, 300mm, 400mm, 500mm and 600mm to determine the initial cracking state according to sudden decrease of the strain gauges’ values. Then the initial cracking load ini P can be gained. Besides, the quarter point singular element approach was used to calculate the stress intensity factors ini I K and ini II K corresponding to ini P in the present study. Moreover, different combinations of ini I K and ini II K were obtained according to different positions of pre-cracks. Correspondingly, the Ⅰ-Ⅱmixed mode fracture initial cracking criterion for concrete can be gained using the curves of track formed by the different combinations of ini I K and ini II K . Through analyzing the curves of track under different specimen heights, it was found that the size effect exists significantly in the specimens with heights from 300mm to 500mm, however, the curves in the 500mm and 600mm specimens approach each other.

Abstract: Compression induced formation of a damage zone, which would result in a shear fault in brittle solids is studied. In a compression test of flawed PMMA, an apparent damage zone composed of large number of scattered cracks, which have no intersection but exist closely with each other, is experienced. The damage zone first appears in a vicinity of tips of artificial flaw and then extends gradually with increase of applied compression. The direction of extension of damage zone is observed to incline about 0 30 from the axis of principal compression. A mechanism of the extension of damage zone with increase of applied compression is discussed using a scattered cracking model. It was found that each crack composing the damage zone has a possibility to open due to crack-to-crack interaction and a localized tensile stress appears both inside and outside of the damage zone. The localized tension appeared in the interior of the damage zone may increase crack density, while that of appeared in the exterior of the damage zone could bring an extension of the damage zone.

Abstract: According to classical definition of crack deformation modes, the constant stress term (Tstress) exists only in presence of mode I. However, some studies show that this term can exist in mode II problems as well; and significantly affect the elastic stress field around the crack tip. Based on the previous analytical results, T-stress changes the photoelastic fringe patterns from symmetric closed shapes to asymmetric and discontinuous loops. In this research, the effects of T-stress on the fringe patterns in mode II cracks is investigated experimentally. Test specimens are Brazilian disks made of polycarbonate, and thermal treatment is performed to remove the residual stresses after generation of the cracks. Observed isochromatic fringes are in good agreement with theoretical predictions. Also, experimental results indicate that this specimen contains a negative T-stress in pure mode II condition.

Abstract: The purpose of this paper is to evaluate the structural capacity of Reinforced Concrete (RC) member retrofitted with Carbon Fiber Sheet (CFS) in order to improve the flexural strength. Eleven RC beam specimens are made and retrofitted with CFS by following the test objective. The main factor in selecting the test parameters is to verify the bond capacity of CFS. Therefore, parameters such as layer number of carbon fiber sheet, strengthening method, bonding ratio (100%-80%), and epoxy type are considered in the test. From the test, all specimens showed little bit different behavior each other. Especially, the flexural capacity was not linearly increased even if the layer number of CFS increased when it was more than two. Also the specimens with the low bonding ratio exhibited low strength as well as premature bond failure on comparing to other specimens.

Abstract: The advancement of proper methodology to determination of VVER reactor pressure vessel (RPV) materials transition behaviour has been followed. The project included selection of proper specimen geometries (standard 10x10x55 mm, sub-size 3x4x27 mm and 5x5x27.5 mm Charpy-V samples) and impact as well as dynamic fracture toughness testing. All the fundamental criterions have been applied to consider an applicability of small-sized specimens to Cr-Mo-V and Cr-Ni-Mo-V steel radiation embrittlement studies. Selected specimen geometries have been found to be fully valid for impact and dynamic fracture data and capable for prediction of standard specimen behaviour from the small specimens. Within testing of irradiated materials, it has been found not fully validity of all the compared transition temperatures.