Levend Parnas

DESIGN OF FIBER-REINFORCED COMPOSITE PRESSURE VESSELS UNDER VARIOUS LOADING CONDITIONS

An analytical procedure is developed to design and predict the behavior of fiber reinforced composite pressure vessels. The classical lamination theory and generalized plane strain model is used in the formulation of the elasticity problem. Internal pressure, axial force and body force due to rotation in addition to temperature and moisture variation throughout the body are considered. Some 3D failure theories are applied to obtain the optimum values for the winding angle, burst pressure, maximum axial force and the maximum angular speed of the pressure vessel. These parameters are also investigated considering hygrothermal effects.

Optimum design of composite structures with curved fiber courses

Abstract In this study, a new methodology for the optimum design of laminated composites with curved fiber courses is presented. The objective of the optimization problem is to minimize the weight of the composite laminate under stress constraints. The Tsai–Hill criterion is employed on the first ply failure basis. Layer thicknesses and fiber angles are represented by bicubic Bezier surfaces and cubic Bezier curves, respectively. Design variables are coordinates of control points of the corresponding Bezier splines. The design variable linking procedure is used in order to reduce the number of design variables further and to provide symmetry in the design. The sequential quadratic programming is used in the optimization. The modeling of the laminate is carried out by using three-node shell finite elements.

Strain gage methods for measurement of opening mode stress intensity factor

In this study, the determination of the opening mode stress intensity factor by using strain gage methods is investigated both experimentally and analytically. The results are compared with the finite element solution. In the experimental program, cracks are opened at the tip of crack starter slot on the standard compact tension test specimens by using Electrical Discharge Machining (EDM) and Wiring Discharge Machining (WDM). Strain gage data from the crack tip region are used to calculate stress intensity factors with some limitations.

Delamination analysis of tapered laminated composites under tensile loading

A study was conducted to analyze tapered composite laminates under tensile loading. A tapered construction made of S2/SP250 glass/epoxy laminate was used to achieve a thickness reduction using three consecutive dropped plies over a distance of 60 ply thicknesses. The principle of minimum complementary potential energy was used to determine interlaminar stresses. The interlaminar peel stress distribution shows a higher tensile intensity at the taper/thin portion juncture. The total strain energy release rate is determined using a simplified membrane model. Results are compared with a finite element simulation.

Athermalization of a forward-looking infrared system

This study presents the athermalization of a forward looking IR system which is one of the tasks of a optomechanical engineer. 3D modeling and optical design of a forward looking IR system are done. Thermal and structural analyses are performed by using the finite element method. Initial conditions and obtained results are verified by a laboratory study. The system parameters are optimized for ensuring the system to perform at different environmental temperatures by determining temperature distributions, expansions and contractions.