Fracture and Strength of Solids VI

Volumes 306-308

doi: 10.4028/

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Authors: Seung Gun Lee, Jong Sung Kim, Jin Seok Park, Tae Eun Jin
Abstract: The multi-pass welding generates residual stress which may change fatigue crack growth rate and impair the lifetime of nuclear welded structures. In this paper, we performed fatigue test with notched specimens and evaluate the effect of residual stress on fatigue crack growth rate of welds. In order to identify the magnitude of residual stress, the residual stress was measured by HDM (hole drilling method) and residual stress analysis was performed by using FEM (finite element method). In order to review the effect of residual stress on fatigue crack growth rate, the fatigue crack growth analysis was also performed to determine the fatigue crack growth curves by using FEM and ASME B&PV Code, Sec.XI, App.A. Finally, as a result of comparison among the fatigue crack growth curves, it is found that the fatigue crack growth rate was quite different according to the crack location even if the residual stresses are considered.
Authors: H.K. Lee, J.C. Huang, G.E. Yang, Hong Gun Kim
Abstract: A relationship of residual stress distribution and surface molding states on polymeric materials is presented in thin-walled injection molding. The residual stress is computed by computational numerical analysis, observed with stress viewer and birefringence. The residual stress on polymeric parts can allude the surface quality as well as flow paths. The residual stress distribution on polymeric parts is related with thickness, gate layout, and polymer types. Molecular orientation on polymeric parts is also important in thin wall injection molding. The residual stress and molecular orientation are related to the surface molding states intimately. Analysis of the residual stress is validated through photo-elastic method and surface molding states..
Authors: S.T. Choi, Jun Yeob Song, Jae Hyun Kim, S. Lee, Y.Y. Earmme
Abstract: The GaAs wafer bonding process is investigated to reduce the mechanical failures of GaAs wafer based on strength design concept. Three-point bending experiment is performed to measure the fracture strength of GaAs wafer, of which cleavage takes place on (110) plane. We propose a simple method for minimizing the thermal residual stress in a three-layer structure, of which the basic idea is to use an appropriate steady-state temperature gradient to the wafer bonding process. The optimum bonding condition of GaAs/wax/sapphire structure is determined based on the proposed method. The effect of material anisotropy on the thermal residual stress is also analyzed by finite element method.
Authors: Guowen Yao, Pei Yan Huang, Chen Zhao
Abstract: Externally bonded carbon fiber reinforced polymer (CFRP) materials are well suited to the rehabilitation and reinforcement of civil engineering structures due to their high specific strength, specific stiffness and corrosion resistance. To probe the fatigue behavior of CFRP strengthened concrete structures, three point bending experiments of reinforced concrete (RC) beams strengthened with carbon fibre laminate (CFL) under constant amplitude loading were performed. The histories of midspan flexibility and bending stiffness of strengthened beams were recorded automatically. And the linear curve between fatigue strength and the logarithm of fatigue life was obtained. The failure modes go through concrete cracking, CFL debonding from concrete and steel bars yielding and fracture with increasing cycles of fatigue loading. Bonded CFL increases the ductility of strengthened RC beam and results in dense distribution of cracks compared with normal RC beam, and it’s bending stiffness at damage state as well. The fatigue damage evolvement shows three stages of nucleation, steady expansion and failure. Then the failure mechanism was studied and a cumulative damage model was proposed to describe the fatigue damage and fracture process of CFL strengthened RC beams under constant amplitude loading.
Authors: Y.H. Kim, S.K. You, Jae Ho Jung, Soon Jong Yoon, Seung Sik Lee
Abstract: Concrete-steel composite members are formed by bonding a steel component, such as an I-section beam, to a concrete component, such as a reinforced concrete slab, so that the two components can act as a unit. The use of such type of composite member becomes main stream of construction technology since it provides efficient load resisting mechanism in structural system. In a composite member, bond between steel and concrete is a crucial factor for the composite action. Usually this bond behavior is achieved by installation of mechanical device so called shear connector. The composite action can be divided into two categories (i.e., full and partial) depending on the shear strength of mechanical shear connector embedded in the concrete, i.e., understanding of shear load resisting mechanism is necessary to develop a new shear connector for better, wider and more efficient application of composite action. For this purpose, the push-out tests are performed for the evaluation of several existing shear connectors including carefully designed perforated shear connector with flange head. One of the purposes of this experimental research is to define the shear resisting mechanism of the proposed new type shear connector. The experimental results show that the degree of composite action using perforated shear connector with flange head is superior to those of existing shear connectors such as a general headed stud, perfobond, etc. The experimental parameters, such as the number of perforated holes, the distance between perforated holes, and the height of shear connector, are carefully chosen for the verification of their effect on the capacity of shear resistance. From this experimental investigation it was found that the mechanical performance of proposed shear connector was efficient as a rigid shear connector.
Authors: Hyung Joong Joo, Seung Sik Lee, Soon Jong Yoon, Ju Kyung Park, Seok Goo Youn
Abstract: Feasibility study on the use of newly developed FRP and concrete composite bridge deck system is conducted. To lengthen the service life of bridge deck, the steel-free bridge deck system is developed. In this deck system, shear connectors between FRP module and concrete are utilized and structural behavior of shear connectors is investigated experimentally. The result of an investigation reveals that the system is promising.
Authors: Sang Kyoon Jeong, Seung Sik Lee, C.H. Kim, Dong Min Ok, Soon Jong Yoon
Abstract: Nowadays, the investigations relating to the FRP re-bars have been increased due to their superior physical and mechanical properties such as environmental resistance, electro-magnetic transparency, and high specific strength and stiffness. In this paper, we present the results of an experimental investigation pertaining to the flexural behavior of concrete beams reinforced with GFRP re-bar bundles for tension and CFRP grids for shear. A total of eight specimens, two pairs of four different shear reinforcement spaces, is loaded to failure under the 4-point bending test set-up. In addition to the experimental investigation, theoretical evaluation is also conducted according to the ACI Committee 440 for all beam specimens. Both experimental and theoretical results such as failure modes and load-deflection relations are compared and good agreements are observed.
Authors: Jeong Hun Nam, Seung Sik Lee, Soon Jong Yoon, Won Sup Jang, S.K. Cho
Abstract: FRP composite materials are widely applicable in the construction industries as a load-bearing structural element or a reinforcing and/or repairing materials for the concrete. In this paper, we presented the flexural behavior of steel reinforced concrete beams reinforced with FRP re-bars manufactured by different fibers but the same vinylester resin. Experimental investigation pertaining to the load-deflection and load-strain characteristics of steel reinforced concrete beams reinforced with FRP re-bars with garnet coated surface is presented and the theoretical prediction is also conducted. In the investigation, the effects of FRP re-bar reinforcement in addition to the steel reinforcement are estimated. The experimental results are compared with theoretical predictions. Good agreements are observed.
Authors: Li Hao, Jian Guo Ning
Abstract: Based on the multi-material Eulerian algorithm, the damage effects of concrete obstruct subjected to underwater explosion shock waves are simulated by using the NM-MMIC code which is a 2D multi-material elastic-plastic hydrodynamics code with C++ language. According to the simulation results of underwater explosion, the optimum charge, the damage degree and the damage laws of obstruct are obtained. The simulation results show a good agreement with that obtained by DYNA2D. Thus the given study indicates that the model and algorithm presented in this paper are reasonable and the simulation method can be used for designing and estimating ammunitions against obstructs in water.
Authors: Qiang Yong Zhang, Wei Shen Zhu, Shu Cai Li, W. Xiang
Abstract: There are large number of intermittently jointed cracks in rockmass, which exist in rockmass as a kind of initial damage. It is their damage, propagation and propagating interaction that result in a variety of failure forms of rockmass. This paper conducts an in depth research on the influence of cracks propagation interaction upon fracture strength of jointed rockmass. A kind of fracture strength model for jointed rockmass is developed under three-dimensional stress conditions. With the utilization of this model in a large-scale highway slope project, the design and construction are effectively performed and remarkable economic benefit has been achieved.

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