Key Engineering Materials Vols. 577-578

Abstract: Plastic film assumes a large role as packaging material in our life. Especially, by lamination which is pasting some kind of simple substances together, plastic films are able to have many kind of function on demand of usage. It is considered that enough high peel strength and tensile strength are needed for liquid package material. And it is considered that low tearing strength is needed for easy open package too. Adhesive existing at interlayer of laminated film, and the amount of adhesive may have effect on these physical properties. In this study, we changed amount of adhesive about laminated film, measured peel strength, tensile strength and tearing strength. And we investigated best suited amount of interlayer adhesive.

Abstract: The Korea Institute of Construction Technology has developed a precast FRP-concrete composite deck to be applied to cable-stayed bridges. This deck is a precast structural system in which concrete is disposed at the upper part and a hollow FRP tube is disposed at the bottom to play the role of tensile reinforcement and form. This paper presents the prototype of the so-developed FRP-concrete composite deck fabricated for trial construction. Electrical resistance sensors and optical fiber sensors were installed on the prototype to evaluate its structural stability and serviceability during the 17 months of operation through a series of field loading tests. From the field loading test results, the FRP-concrete composite deck was verified to secure sufficient structural stability and serviceability along the 17 months of operation even after the repeated passage of the heavy construction trucks. Besides, it appeared also that, for long-term monitoring, the optical fiber sensor provided more reliable measurement than the electrical resistance sensor glued to the structure.

Abstract: In this paper, a numerical study, on the compressive behaviour of stiffened composite panels with skin-stringer debonding has been carried out. The analysis has been performed by adopting a novel robust (mesh and time step independent) finite elements based numerical model on a single stiffener panel with an artificial debonding. In order to prove the effectiveness of the proposed numerical tool, the results in terms of debonded area growth and compressive load versus applied displacement, have been compared with experimental data available in literature.

Abstract: Effective modeling of ice material behavior requires treatment of both damage and fracture. In this paper, a discussion of local ice damage and fracture processes observed during laboratory-scale indentation experiments conducted on unconfined polycrystalline ice using a spherical indenter is provided. Particular emphasis is placed on the interplay between fracture and extrusion processes corresponding to the failure of ice under a single zone of high contact pressure. Simulations have been conducted using a continuum damage mechanics user-material routine in conjunction with element removal techniques to simulate pressure-softening and discrete fracture processes, respectively. Simulation results provide good agreement with test data and provide important insights into interplay between damage and fracture mechanisms associated with compressive ice failure. Finite element modeling was found to work well for modeling pressure softening effects and for replicating the effects of discrete fracture events. For interactions involving multiple failure events, further work is needed to develop models that account for random aspects of fracture associated with flaw structure, contact geometry and the geometry of individual spalls.

Abstract: The mechanisms of spalling and melting in nanocrystalline Pb under shock loading are studied by molecular dynamics simulations. Our results show that grain boundaries have significant influences on spalling behaviors in cases of classical spallation and releasing melting. In these cases, cavitation and melting both start on grain boundaries, and they display mutual promotion: melting makes the voids nucleate at smaller tensile stress, and void growth speeds melting. Due to grain boundary effects, the spall strength of nanocrystalline Pb varies slowly with the shock intensity in cases of classical spallation. In cases of releasing melting and compression melting, spall strength of both single-crystalline and nanocrystalline Pb drops dramatically as shock intensity increases.

Abstract: Rubber-sleeved headed stud shear connector is flexible shear connector used in steel-concrete composite structures. In this work, nonlinear finite element model has been developed to simulate the failure process of the shear connector under shear loading. The stress distribution, deformation, crack propagation and failure mode were analyzed. The material nonlinearities of rubber, headed stud, concrete were considered in the material model. The rubber was assumed as a perfect material with no defect, and a modified reduced polynomial form of strain energy including an energy limiter and a new constant was introduced into the user material subroutine VUANISOHYPER-INV of ABAQUS software. Damaged plasticity model was used to model the concrete material. A tri-linear elastic-plastic curve was used in stud material model. Comparing the results obtained from the finite element analysis with those from push-out test, good agreement is highlighted in the capacity, ductility and failure mode of rubber-sleeved headed stud shear connector.

Abstract: Recently, various types of slab systems which can reduce self-weight of slabs have been studied as the height and width of building structures rapidly increase. A hollow slab system is widely known as one of the effective slab system which can reduce self-weight of slab. According to previous studies, the hollow slab with donut type hollow sphere had enough flexural strength. On the other hand, there were some differences in flexural stiffness and deflection between general RC slab and donut type hollow slab. The deflection of hollow slab was influenced by the shapes of hollow spheres due to its different second moment of inertia and amount of concrete surrounding bottom re-bar. Especially, the cracking behaviors also influence the deflection of slab. General RC slab deflection has been sufficiently investigated and some models to consider the crack behavior such as crack width, crack space, tension stiffening effect, bond-slip relationship. However, there is no study about the crack behavior on the hollow slab. Therefore, the purposes of this paper are to presents the cracking behavior of donut type hollow slab and to evaluate the deflection considering the crack behavior under flexural load.

Abstract: For the components working in high temperature and enduring fatigue loading, the fatigue fracture properties will be reduced remarkably when the working temperature is higher than the critical temperature of creep-fatigue interaction T_c of the material. In consequence, the damage mechanism from creep-fatigue interaction becomes more complex. A method is presented in this paper to determine the T_c of a nickel-based powder metallurgy superalloy. Pure fatigue crack growth and creep-fatigue crack growth tests were conducted in several different elevated temperatures. The fracture mechanism was investigated via observing the fractographic characteristics using scanning electron microscope (SEM). The test results show that the T_c of this superalloy is a little bit lower than a half of the melting temperature T_m.

Abstract: Shield structure based on ceramic coating on aluminum bumper was designed, and a series of hypervelocity impact tests were practiced with a two-stage light gas gun facility. Impact velocities were varied between1.5km/s and 5.0km/s. The diameter of projectiles were 3.97mm and 6.35mm respectively. The impact angle was 0°. The damage of the ceramic coating on aluminum bumper under hypervelocity impact was studied. It was found that the ceramic coating on aluminum bumper could help enhancing the protection performance of shield to resist hypervelocity impact. The results indicated when the ceramic coating is on the front side of aluminum bumper, it was good for comminuting projectile and weakening the kinetic energy of projectile. For a certain aluminum bumper, existing a critical thickness of ceramic coating in which capability of Whipple shield to resist hypervelocity impact is the best. On this basis, the proposal of the optimum design for ceramic coating on aluminum bumper was made.

Abstract: Closed cracks, which stay in contact unless the excitation exceeds a certain threshold, exist as great menace to structures. Since nonlinear response is more sensitive to micro damage than conventional linear approaches, analyzing the nonlinear part of the collected response of structures to an input ultrasonic excitation is more promising in damage detection. In this paper, in order to image the location of a closed crack, an instantaneous baseline measurement is adopted and the nonlinear response is extracted by using scaling subtraction method. A three-dimensional finite element model of a plate with a closed crack is developed and the behavior of the closed crack is simulated with nonlinear springs at the crack interfaces. A network of actuators and sensors which constitutes of two arrays of surface-bonded piezoelectric transducers is built. The instantaneous baselines of each path are collected when the model is excited with low amplitude excitation. To diagnose the closed crack, a higher amplitude excitation over the threshold is applied to the model and the response signals of each path are recorded. The result shows that the differences caused by the crack can be observed from the scaling subtraction of these two recorded responses and the location of closed crack can be accurately imaged.