Optimization of Variable-Stiffness Panels for Maximum Buckling Load Using Lamination Parameters

AIAA Journal ◽  
2010 ◽  
Vol 48 (1) ◽  
pp. 134-143 ◽  
Author(s):  
Samuel T. IJsselmuiden ◽  
Mostafa M. Abdalla ◽  
Zafer Gurdal
Keyword(s):  
Variable Stiffness ◽  
Buckling Load ◽  
Lamination Parameters

Design of Variable Stiffness Cylinder with Holes Under Bending for Maximum Buckling Load Using Lamination Parameters

2019 ◽  
Author(s):  
Mazen Albazzan ◽  
Brian Tatting ◽  
Ramy Harik ◽  
Zafer Gürdal ◽  
Adriana Blom-Schieber ◽  
...  
Keyword(s):  
Variable Stiffness ◽  
Buckling Load ◽  
Lamination Parameters

Structural Analysis of Variable Stiffness Laminated Plates Using First-Order Shear Deformation Theory

2014 ◽  
Author(s):  
A. H. Akbarzadeh ◽  
M. Arian Nik ◽  
D. Pasini
Keyword(s):  
Transverse Shear ◽  
Deformation Theory ◽  
Shear Deformation Theory ◽  
Variable Stiffness ◽  
Buckling Load ◽  
Shear Stresses ◽  
Critical Buckling Load ◽  
First Order ◽  
Stiffness Design ◽  
Transverse Shear Stresses

Constant and variable stiffness strategies have been developed to design a composite laminate. With the former, each layer is designed with straight fibers that have the highest stiffness and strength in the fiber direction. With the latter, on the other hand, the stiffness can change within each layer by placing the fibers along a curvilinear fiber path. A variable stiffness design results in improved structural performance, as well as opens up opportunities to search for trade-off among structural properties. During the manufacture of a variable stiffness design with Automated Fiber Placement, certain defects in the form of gaps and overlaps could appear within the laminate and affect the laminate performance. In this study, we use the first-order shear deformation theory to assess the effect of transverse shear stresses on the critical buckling load, free and forced vibration of a variable stiffness laminate with embedded defects, an issue so far rarely examined in literature. The governing differential equations for the static analysis are first derived. A semi-analytic solution is then obtained using the hybrid Fourier-Galerkin method and the numeric time integration technique. The eigenvalue analysis is also conducted to determine the fundamental frequency and critical buckling load of the plate. It is found that the behavior of a variable stiffness plate is much more affected by the shear stresses than a constant stiffness plate. Ignoring the effect of transverse shear stresses results in 34% error in the predicted buckling load of a variable stiffness laminate with overlaps and a length-to-thickness ratio of 10.

Size-dependent behavior of laminates with curvilinear fibers made by automated fiber placement

2015 ◽  
Vol 22 (2) ◽  
pp. 157-163 ◽  
Author(s):  
Mahdi Arian Nik ◽  
Larry Lessard ◽  
Damiano Pasini
Keyword(s):  
Variable Stiffness ◽  
Buckling Load ◽  
Fiber Placement ◽  
Plate Size ◽  
Load Increase ◽  
Automated Fiber Placement ◽  
Fiber Path ◽  
Turning Radius ◽  
Curvilinear Fibers ◽  
Minimum Turning Radius

AbstractVariable stiffness laminates can be manufactured using curvilinear fiber paths. A curvilinear fiber path is generally defined based on the plate size and has a curvature that is dependent on the plate size. In practice, however, the fiber path must satisfy manufacturing constraints, such as the minimum turning radius imposed by the automated fiber placement machine, thereby limiting the possible amount of fiber steering. In this work, we studied the effect of the plate size on the structural properties of a plate manufactured with curvilinear fibers. We considered four plate sizes, which were designed by a constant curvature fiber path. We optimized the plates for both maximum buckling load and in-plane stiffness. The results showed that the in-plane stiffness of the plate was not controlled by the plate size, whereas the buckling load was highly affected by the curvature of the fiber path. Hence, the potential of a buckling load increase reduced for plate sizes smaller than the minimum turning radius. In addition, for a given maximum curvature of the fiber path, the influence of a complex layup on the buckling load was marginal.

Determination of the Buckling Load for Columns of Variable Stiffness

1949 ◽  
Vol 16 (4) ◽  
pp. 406-410
Author(s):  
C. C. Miesse
Keyword(s):  
Lower Bounds ◽  
Axial Loading ◽  
Variable Stiffness ◽  
Buckling Load ◽  
Upper And Lower Bounds ◽  
Variable Section ◽  
Rayleigh Principle

Abstract A method is given for determining both upper and lower bounds on the critical or buckling load for variable-section columns with axial loading. This method, which is an extension of the Rayleigh principle, is illustrated by three examples.

Optimisation of Variable Stiffness Plates

2016 ◽  
Vol 828 ◽  
pp. 27-48 ◽  
Author(s):  
Paul M. Weaver ◽  
Zhang Ming Wu ◽  
Gangadharan Raju
Keyword(s):  
Composite Laminates ◽  
Composite Structures ◽  
Variable Stiffness ◽  
Feasible Region ◽  
Lamination Parameters ◽  
Aspect Ratios ◽  
Design Variables ◽  
Stiffness Matrices ◽  
Out Of Plane ◽  
Component Material

Variable angle tow (VAT) describes fibres in a composite lamina that have been steered curvilinearly. In so doing, substantially enlarged freedom for stiffness tailoring of composite laminates is enabled. VAT composite structures have been shown to have improved buckling and postbuckling load carrying capability when compared to straight fibre composites. However, their structural analysis and optimal design is more computationally expensive due to the exponential increase in number of variables associated with spatially varying planar fibre orientations in addition to stacking sequence considerations. In this work, an efficient two-level optim isation framework using lamination parameters as design variables has been enhanced and general ised to the design of VAT plates. Explicit stiffness matrices are found in terms of component material invariants and lamination parameters. The convex hull property of B-splines is exploited to ensure point-wise feasibility of lamination parameters. In addition, a small set of explicit closed-form expressions is used to define the feasible region of two in-plane and two out-of-plane lamination parameters, which are used for the design of orthotropic laminates. Finally, numerical examples of plates under compression loading with different boundary conditions and aspect ratios are investigated. Reliable optimal solutions demonstrate the robustness and computational efficiency of the proposed optimisation methodology.

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