Advances in Fracture and Failure Prevention

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Authors: Jae Ho Jung, Soon Jong Yoon, S.K. You
Abstract: In this paper, the buckling behavior of elastically restrained orthotropic web plates is investigated. In general, the pultruded FRP structural member is composed of flat plate elements and each plate element is elastically restrained against rotation by adjacent plate components. For finding the local buckling strength of composite flexural member considering the elastic restraint at the juncture of plate components, the orthotropic web plate is modeled as an elastically restrained orthotropic plate under linearly distributed in-plane forces. For the derivation of buckling equation, the power series solution technique is employed. For the plate having different mechanical properties, the parametric studies are conducted by varying the degree of restraint along the longitudinal edge under compression. By using the results obtained, simplified form of equation is also developed so that the practicing engineers can evaluate the buckling stress of such a plate for the preliminary design of FRP flexural members.
Authors: Soon Jong Yoon, Jae Ho Jung, Won Sup Jang
Abstract: This paper presents the analytical investigations pertaining to the elastic buckling behavior of orthotropic composite plates. By the pultrusion process the structural shapes composed of orthotropic plate components are readily available in the construction market. When the member is utilized for the flexure, lateral-torsional buckling and local buckling behaviors must be taken into consideration. In the local buckling analysis, flange and web local buckling analyses must be conducted in the design of such a member. For finding the web buckling strength, the buckling equation for the orthotropic plate under linearly distributed in-plane forces is derived by using the Rayleigh-Ritz method. The boundary conditions of plate are assumed that the loaded edges are simply supported and the unloaded edges are simply supported or fixedly supported. The buckling coefficient of a plate having different orthogonal mechanical properties is found by using the numerical technique and the minimum buckling coefficient is suggested. In addition, simplified form of equation for predicting the minimum buckling coefficient for the plate is proposed. Brief discussion on the design criteria relating to the web local buckling is also provided.
Authors: S.K. Jeong, Soon Jong Yoon, Sun Kyu Cho
Abstract: The problem addressed in this paper is the elastic local buckling of thin-walled compression members whose plate components are tapered in thickness along the longitudinal direction. In the design of structural system in construction, shipbuilding, and aerospace industries, such structural plate components are frequently encountered. The elastic buckling analysis of transversely isotropic plates with varying thickness and various boundary conditions is performed to derive the buckling equation of thin-walled members composed of tapered plate components. In the analytical solution, the energy approach is adopted. The analytical results are presented in a graphical form in which the plate buckling coefficients are suggested with respect to the width ratio of plate elements and the degree of taper. In addition, using the buckling equations of plates with specific boundary conditions, the simplified form of equation for the local buckling coefficient of structural members such as L-section, T-section, and Box-section is suggested.
Authors: Sung Hyuk Lee, Nak Sam Choi
Abstract: To analyze the bending collapse behavior of an aluminum square tube under the bending moment load, a finite element simulation for the four-point bending test has been performed. Using an aluminum tube beam specimen partly inserted with two steel bars, local buckling deformation near the center of the tube beam was induced. Simulated moment-rotation angle curve obtained during the post-collapse period of the aluminum tube with steel bars were in good agreement with experimental result, which was comparable to the result obtained from Kecman's theory. Using a combination of the four-point bending test and its finite-element simulation, analysis of the local buckling and the bending collapse behavior of an aluminum tube beam could be quantitatively accomplished.
Authors: Chong Ge Wang, Zhao Qing Song, Wei Zhong Chen, Quan Sheng Liu, Chien Hsin Yang
Abstract: This paper introduces temperature effect to rock model. It sets up a thermo-visco-elastic-plastic rock model. Based on the rock model which consists of spring, dashpot and plastic elements under the condition of un-axial compression, the behaviors of the thermo-visco-elastic-plastic in rock are discussed, and the equations of the constitutive, creep, unload and relaxation have been obtained. This model can reflect the rock or rock mass average thermo-rheology character. Meanwhile, this study gives a explanation of the significances of this kind of model in the practical use.
Authors: Hong Gun Kim
Abstract: A stress analysis has been performed to evaluate the thermally induced elastic stresses which can develop in a short fiber composite due to coefficient of thermal expansion (CTE) mismatch. An axisymmetric finite element model with the constraint between cells has implemented to find the magnitude of thermoelastic stresses in the fiber and the matrix as a function of volume fraction, CTE ratio, modulus ratio, and fiber aspect ratio. It was found that the matrix end regions fall under significant thermal stresses that have the same sign as that of the fibers themselves. Furthermore, it was found that the stresses vary along the fiber and fiber end gap in the same manner as that obtained in a shear-lag model during non-thermal mechanical loading.
Authors: Z.S. Shao, L.F. Fan, Tie Jun Wang
Abstract: Analytical solutions of stress fields in functionally graded circular hollow cylinder with finite length subjected to axisymmetric pressure loadings on inner and outer surfaces are presented in this paper. The cylinder is simply supported at its two ends. Young's modulus of the material is assumed to vary continuously in radial direction of the cylinder. Moreover, numerical results of stresses in functionally graded circular hollow cylinder are appeared.
Authors: Young Doo Kwon, S.W. Choo, J.K. Lee, J.Y. Kim
Abstract: Generally, structures used in outer space are subjected to severe situations, including sublimation, a strong evaporation of lubricants, thermal stresses, high temperature gradients, irradiation, impact from microscopic meteorites, and other factors. Recently, various kinds of coatings have been applied to structural parts under heavy contact stresses to ensure a longer wear-free life and/or reduce the friction coefficients. Accordingly, the current study applied FEM to analyze space parts with a coating layer thermo-mechanically subjected to a contact load. First, a steady state temperature distribution of the space part was obtained, then a quasi-static external load was applied. Thereafter, the total solution was computed and the thermal strain subtracted to obtain the mechanical strains for determining the stresses of the individual part. When using FEM, the model needs to discretize into many sub-domain finite elements. Since the difference, however, in the dimension between the coating layer and the substrate is so large, the analysis needs to be considered carefully. Consequently, the problem was analyzed in two steps. First, the whole model was analyzed using rather coarse meshes, then a small region was cut near the loading point and analyzed using very fine meshes. This method is based on Saint-Venant's principle. Finally, the effect of a thermal load on the stress of a space part with a coating layer was checked with and without cracks in the substrate. Accordingly, the results demonstrate the stresses on a space part under a thermo-mechanical load, along with the effects of various coating materials and a crack in the substrate on the stress distribution.
Authors: Kwang Joon Yoon, Young Suk Kim, Young Bae Kim, J.D. Lee, Hyun Chul Park, Nam Seo Goo, J.H. Lee
Abstract: In this paper, a simple conformal load-bearing antenna structure smart skin with a multi-layer sandwich structure composed of carbon/epoxy, glass/epoxy, and a dielectric polymer was designed and fabricated. The mechanical properties of each material in the designed smart skin were obtained from experiments. Tests and analyses were conducted to study the behavior of the smart skin under compressive loads. The designed smart skin failed due to buckling before compression failure. The stresses of each layer and the first failed layer of the smart skin were predicted using MSC/NASTRAN. The finite element model was verified by comparing the numerical results from geometrical linear/nonlinear analyses with the measured data. The numerically predicted structural behavior of the smart skin agreed well with the experimental data. The results showed that the carbon/epoxy layer took charge of most of the compressive load, and the first failure occurred in the dielectric layer while the other layers remained safe. A numerical model was used to obtain design data from the parametric study. The effect of changing the design variables on the buckling and compressive behavior of the smart skin was also investigated. As a result, it was confirmed that the transverse shear moduli of the honeycomb core had a serious impact on the buckling load of the smart skin when the shear deformation was considerable.
Authors: Hironobu Nisitani, T. Teranishi, K. Fukuyama
Abstract: It is important to know the stress intensity factor of a circumferential crack emanating from the cavity, because in some cases the fatigue strength of metals is affected by the existence of an internal cavity or an inclusion. Recently a method for calculating the highly accurate values of stress intensity factors was proposed by H. Nisitani, based on the usefulness of the stress values at a crack tip calculated by FEM. This method is called the crack tip stress method. In this study, the crack tip stress method is applied to the problem of an infinite solid having two cavities with a circumferential crack emanating from the cavity subjected to tension. The accuracy of the crack tip stress method was discussed based on some values obtained by the body force method. Moreover, a simple method for calculating the stress intensity factor of this problem was presented.

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