Y. W. Kwon

Underwater shock response of a cylinder subjected to a side-on explosion

Abstract The nonlinear dynamic response of a cylinder subjected to a side-on, far-field underwater explosion was studied using both numerical and experimental techniques. Both ends of the cylinder were closed with thick flat plates. An explosive charge was located 25 feet (7.62 m) from the cylinder on a line perpendicular to the cylinder axis and equidistant from the cylinder ends. Comparison of axial and hoop strains was made between the strain gage measurements and the numerical results at several different locations on the cylinder. Overall, the comparison was in a good agreement. However, it was found that there were asymmetric strain gage data from the experiment. With the postulation of cylinder rotation so that the charge was not located at center of the cylinder length, an additional numerical study was undertaken to investigate the effect of the rotation on the strain distributions. This study showed improvements of the numerical results compared to the experimental data. The numerical study indicated that the dynamic motion of the cylinder has an accordion mode, a breathing mode and a whipping mode.

Micromechanics model for damage and failure analyses of laminated fibrous composites

Abstract A micromechanics model was developed for damage and failure analyses of laminated fibrous composite structures. The micromechanics model computed stresses and strains at the fiber and matrix level, as well as the smeared composite stresses and strains. Damage and failure criteria used in the present study were based on the fiber and matrix stresses rather than smeared composite stresses. Progress of damage, e.g. matrix cracking and fiber breakage, as well as final failure loads were computed from the present model which was incorporated into a finite element analysis program. Some example problems were solved using the present model and the predicted results were compared to experimental results. The two results agreed very well. The model allowed the load transfer from cracked matrix to surrounding fibers until the fibers came to failure.

Analysis of layered composite plates using a high-order deformation theory

Abstract A high-order plate bending displacement field is developed for the analysis of layered composite plates. The parabolic distribution of the transverse shear strains is considered in the equation, and a mixed finite element model is introduced from the equation. The present finite element model is applied to thin and thick layered composite plate bending problems and its solutions are compared with threedimensional elasticity solutions.

Matrix damage of fibrous composites: Effects of thermal residual stresses and layer sequences

Abstract A simplified micromechanics model and a damage evolution function are incorporated into a finite-element analysis program for laminated fibrous composite structures in order to investigate the effects of microscale damages on the structural response. The computer program can analyze both fiber failure and matrix cracking. However, the present study focuses on matrix cracking. In the present study, two kinds of problems are solved using the computer program. The first study is to investigate effects of contiguous stacking of 90 ° layers in cross-ply composites on reduction of composite stiffness. The analyses show that more contiguous stacking of 90 ° layers in cross-ply composites causes a greater stiffness reduction for the same amount of matrix cracking. The second study investigates the effect of thermal residual stresses on the composite stiffness reduction. The results show that the thermal residual stresses play an important role in matrix cracking of cross-ply, fibrous composites.

MICROMECHANICAL MODEL FOR THERMAL ANALYSIS OF PARTICULATE AND FIBROUS COMPOSITES

Thermal stresses occur at the micromechanical level of a particle-/fiber-reinforced composite caused by the mismatch of coefficients of thermal expansion (CTE) of the constituent materials like the particle/fiber and the matrix binder. The stresses affect the service envelope of a composite structure when it is subject to an external load. Thus, this ankle presented a simplified, analytical, three-dimensional, micromechanical model so as to compute microthermal stresses occurring in the constituent materials as well as the effective CTE of a composite based on their materials properties. The analytical solutions for both particulate and fibrous composites were compared to the results obtained from finite element analyses as well as other results if available. The comparison of the effective CTEs and the microthermal stresses between the present solutions and the finite element results showed an excellent agreement. In addition, a parametric study was conducted in order to determine the effects of each par...

Multilevel, micro/macro-approach for analysis of woven-fabric composite plates

An approach wasdeveloped to analyze woven-fabric composite structures based on microlevel properties of the fiber and matrix materials. The approach is based on bilateral relationships among the fiber and matrix materials, unidirectional composites (strands), woven fabric layers, and laminated composite structures, as given in the sequence. Simplified analytical models were developed for the relationship between any two subsequent levels. The approach can predict the stiffness, strength and progressive failure of woven-fabric composite structures using material properties of the fiber and matrix materials, their volume fractions, and the information for weaving and lamination. Progressive failure can be described at the fundamental level like fiber failure, matrix failure and interface failure. Example problems were presented for evaluation of predicted stiffness, strength, and failure for plain-weave composite plates subjected to inplane or bending loads.

Finite element analysis of dynamic instability of layered composite plates using a high-order bending theory

Abstract A high-order deformation theory of plate bending has been developed for the static bending analysis of layered composite plates in a previous work. In the present paper, a dynamic instability analysis based on the same high-order deformation theory is presented. The boundaries of the principal instability domains are studied for different cases of plates. The comparison between the high-order theory and the classical theory is presented for various thickness-to-side length ratios, different boundary conditions, different longitudinal to transverse elastic moduli ratios, and different numbers of layers.

Study of damage evolution in composites using damage mechanics and micromechanics

A numerical modeling technique was presented to simulate, predict and evaluate progressive damage or failure in a composite structure subjected to an external loading. To this end, a micro/macromechanical approach was proposed along with damage mechanics at the microlevel. The micro/ macromechanical model utilized both the macromechanical analysis and the micromechanical analysis in tandem. The continuum damage mechanics was applied to the microlevel stresses-strains in order to predict damage evolution in a composite structure from the initiation of damage through to complete failure of the structure. Crack initiation and growth in a particulate composite with stress concentration was simulated using the proposed technique, and the results were compared to experimental data. The comparison showed a very good agreement.

Dynamic finite element analysis of laminated beams with delamination cracks using contact-impact conditions

A new finite element modeling technique is presented to investigate the static and dynamic behavior of laminated composite beams with partial delamination. In this study, a recently developed rectangular beam element is used. The element has lateral and axial displacements as degrees of freedom, but not rotation. For simplicity, linear shape functions are used for the beam element. As a result, the element has six degrees of freedom, four of which are the axial nodal displacements at the corner points and the other two are the lateral displacments at the ends. In addition, contact-impact conditions are applied to the finite element modeling to avoid overlapping of the upper and lower portions of a delaminated section. The numerical study shows that, depending on existence of an embedded delamination crack and its size, the response is different for a beam with a crack and subjected to a short impulse load. Hence, the present modeling technique may be used for detection of an embedded delamination crack.

Comparison of USA-DYNA finite element models for a stiffened shell subject to underwater shock

Abstract A numerical study was conducted for simplified finite element modeling of stiffened structures under a dynamic loading. The study considerd submerged structures subject to an underwater explosion. The objective of this study was to develop a finite element modeling technique which is computationally efficient and still accurate in terms of the structural dynamic response. This paper investigated techniques for smearing of stiffeners, represenation of a cylindrical shell by a beam with surface of revolution (SOR), and interface of a cylindrical shell with a SOR beam. The advantage and disadvantage: of those techniques in conjunction with an explicit time-integration scheme were also discussed.