Key Engineering Materials Vols. 297-300

Abstract: The local buckling analysis of thin walled member is generally conducted by modeling each plate component as an isolated plate with elastically restrained boundaries. When this analytical model is used for the orthotropic flexural members, it is necessary to obtain the degree of elastic restraint provided by adjacent plate. In this study, the equation to find the coefficient of elastic restraint by adjacent plate components of an orthotropic box-shape flexural member was derived by employing the energy approach, and the factors affecting the elastic restraint were briefly discussed. Using the suggested equation, the coefficient of elastic restraint was calculated, and the local buckling analysis was conducted according to the stepwise analytical procedure published by the authors. The theoretical predictions were in good agreement with results obtained by the closed-form solution. The local buckling strength of an orthotropic box-shape flexural member can be easily obtained through stepwise analytical procedure with the proposed equation that accounts for the effect of elastic restraint imposed by adjacent plate components.

Abstract: Pultruded fiber reinforced polymer (FRP) structural members have been used in various civil engineering applications. T-shapes are commonly used for chord members in trusses and for bracing members. In these cases, T-shapes are mainly subjected to axial forces, and stability of a member is one of the major concerns in the design. Due to the monosymmetry existing in the cross-section of T-shapes, T-shapes are likely to buckle in a flexural-torsional mode. An energy solution, using the Ritz method, to the buckling problem of a pulturuded T-shape under uniform compression is derived based on a composite thin-walled beam theory developed by Bauld and Tzeng. The solution accounts for the bending-twisting and bending-extension coupling effects. The derived energy solutions are compared to the experimental results of buckling tests conducted on seventeen pultruded T-shapes. It is found that the ratios of the experimental to analytical results are in the range of 1.00 to 1.32.

Abstract: The shortcoming of conventional SLT (Shear Lag Theory) is due to the neglect of stress transfer across the fiber ends, which results in the inaccurate stress variation for the fiber when the fiber aspect ratio is small in elastic loading. Thus a new model called NSLT (New Shear Lag Theory) is developed considering the stress concentration effects that exists in the matrix regions near fiber ends. In this paper the prediction of elastic composite modulus is presented to evaluate the stress transfer mechanism using NSLT. A micromechanical FEA (Finite Element Analysis) model with axisymmetry is implemented to verify the results of fiber stresses and interfacial shear stresses. It is found that the proposed model gives a reasonable prediction compared with the results based on other models.

Abstract: First, the characteristics of thermal residual stress in randomly oriented short δ-Al2O3 fiber reinforced aluminum alloy composites were analyzed by an elasto-plastic finite element method regarding the effect of the variation in short fiber orientation. Then, the effective moduli and initial tensile stress-strain curves of the composites were simulated by finite element method with the thermal residual stress taken into account. It is concluded that the simulated results obtained with thermal residual stress contained agree with corresponding experimental results better than those obtained in thermal residual stress-free cases.

Abstract: This paper deals with the hygrothermal stress singularity induced at the interface corner between the epoxy coating layer and the concrete substrate as the coating layer absorbs hot moisture from the ambient environment. The epoxy layer is assumed to be a linear viscoelastic material and to be theromorheologically simple. It is further assumed that moisture effects are analogous to thermal effects. The viscoelastic boundary element method is employed to investigate the behavior of interface stresses. The order of the singularity is obtained numerically for a given viscoelastic model. The numerical results exhibit the relaxation of interface stresses and large stress gradients are observed in the vicinity of the free surface. Since the exceedingly large stresses cannot be borne by the epoxy coating layer, local yielding or the delamination can occur at the interface corner.

Abstract: In this paper a transient dynamic finite element analysis is presented to study the response of centrally impacted delaminated composite pretwisted cylindrical shells. An eight noded isoparametric plate bending element is employed in the finite element formulation. Effects of transverse shear deformation and rotary inertia are included. To satisfy the compatibility of deformation and equilibrium of resultant forces and moments at the delamination crack front a multipoint constraint algorithm is incorporated. The modified Hertzian contact law which accounts for permanent indentation is utilized to compute the contact force, and the time dependent equations are solved by Newmark’s time integration algorithm. Parametric studies are performed in respect of relative size of delamination and angle of twist for graphite-epoxy composite cylindrical shallow shells subjected to low velocity normal impact.

Abstract: The goals of this paper are to identify the impact damage behavior of plain-weave E-glass/epoxy composites and predict the fatigue life of the composites with impact-induced damage under constant amplitude loading. To identify these behaviors, the low velocity impact and fatigue after impact tests are performed for glass/epoxy composites having two types of fiber orientations. The impact damage behavior is dependent on the fiber orientation of the composites. The fatigue life of the impacted composites can be identified through the prediction model, which was proposed on the carbon/epoxy laminates by authors regardless of fiber orientations.

Abstract: Impact behavior of simply-supported circular thin plates made of PC/ABS (50/50) blends tested at room temperature by use of instrumented drop weight impact apparatus under different speeds: 2, 3, and 4m/sec has been studied. The blends have 10wt% content of rubber with rubber particle diameter of 270nm and of 150-170nm distributed in ABS. Features of the target are viewed to describe definite alteration of the plates induced by a hemispherical tip-ended cylindrical impactor and effect of rubber particle size distributed in the blends. It was found that the blends with a rubber particle diameter of 150-170nm were not in shattering and exhibited a unique crack shape at speed of 3m/sec. Simulation of the impact test was also performed using dynamic explicit finite element code of MSC. Dytran. In the simulation, the material was assumed isotropic and mass served as a rigid surface and an available material model in the finite element system, called piecewise linear plasticity, referring to a yield model of the von Mises was applied in the simulation for describing the large strain, non-linear behavior of the polymeric materials. Maximum plastic strain failure criterion was then used to simulate the impact failure. Contact between the impactor and the plate was applied and friction coefficient µ between the impactor and the plate was neglected. In order to study effect of friction coefficient value, additional simulation of the impact test has also been performed using µ = 0.3. Impact force-time histories of the blends obtained from the simulation were then verified to the impact test results and pointed out an evaluation of the use of the finite element analysis for predicting behavior of the blends under the impact loading.

Abstract: The objectives of this study are to evaluate the internal damage and compressive residual strength of composite laminate by impact loading. To investigate the environmental effects, as-received and accelerated-aged glass/phenolic laminates are used. UT C-Scan is used to determine the impact damage characteristics and CAI tests are carried out to evaluate quantitatively the reduction of compressive strength by impact loading. The damage modes of the woven glass/phenolic laminates are evaluated. In the case of the accelerated-aged laminates, as aging time increases, initial failure energy and residual compressive strength decrease.

Abstract: A spacer grid assembly is one of the main structural components of the fuel assemblies of Pressurized light Water Reactors. The spacer grid assembly is structurally required to have enough buckling strength under various kinds of lateral loads acting on the fuel assembly so as to keep the fuel assembly straight. The structural performance of the spacer grid assembly is characterized in terms of its dynamic crush strength, which is usually acquired from the test. In this study, a dynamic buckling test and a finite element analysis on the KAERI designed spacer grid assembly are carried out. The pendulum-type tester was used in the test. In the finite element analysis, we proposed an analysis methodology that could predict the dynamic failure behavior of the spacer grid assembly using a commercial finite element code ABAQUS/explicit with appropriate boundary conditions. As a result of the comparisons, the analysis result is in good agreement with the test result to within a 10% difference range. Therefore, we could predict the dynamic behaviors of a spacer grid assembly in advance before performing the dynamic buckling test.