Fatigue Loading Considerations for a Composite Cylindrical Shell with a Square Cutout
To determine strength allowables for cylinders–such as aircraft fuselages–made of fiber-matrix composites, practical analytical tools are needed to determine damage extent and residual strength around cutouts. A higher-order shell theory is used to analyze compressive and tensile loads on a graphite/epoxy laminated cylinder containing a square cutout. Failure in the fiber, matrix, or lamination is determinated by the Hashin failure criterion and modeled by reducing the appropriate stiffness terms. This results in a redistribution of stress, leading to further failure. Under fatigue loads, graphite/epoxy will lose stiffness as cycles increase. To model this effect of cyclic loading, the stiffness matrix is further reduced at the beginning of each cycle. Therefore, the static analysis can be used to predict damage under fatigue loading by representing several thousand fatigue cycles in a single computational cycle. In compression loading, the reduction in stiffness ultimately leads to geometric instability, or collapse. In tension, the reduction is stiffness–to account for fatigue–increases the displacements, but not the stress. Therefore, a strain-based criterion is added to induce macromechanical failure from the cyclic loading. The material damage propagates until failure of the curved panel occurs. The objective is not to model the micromechanical failure in the structure, but rather to determine the damage extent, stress redistribution, and residual strength of composite cylinders under fatigue loading.
The Effects of Delamination on the Fatigue Behavior of Composite Structures
The aim of the present study is to investigate the role played by delamination on the fatigue behavior of centrally holed CFRP laminates. To reach this objective, both theoretical and experimental studies were performed. As to the theoretical analysis and the relevant numerical predictions of the 3D state of stress, the study proposes the use of a finite element procedure based on a multi-layer higher-order laminate theory developed by the authors in conjunction with the application of an interlaminar failure criterion. The approach assumes that significant information on the fatigue life of holed laminate can be obtained by performing a static prediction only. Two types of rectangular laminates with stacking sequences [+45)4/(-45)4] s , and [0/90] 3 manufactured with T300/934 are examined. The static and the fatigue failure of the above mentioned laminates were then investigated in a series of experiments in order to verify the initiation of delamination both in the static case and during the fatigue loading process, ultrasonic nondestructive inspections were also made. The obtained results show a significant correspondence between the experimental static and fatigue behavior of the laminates and the theoretical predictions. They show also that an efficient numerical tool of the 3D state of stress prediction is used.
Flow in a branching open channel: a review
Branching channel flow refers to any side water withdrawals from rivers or main channels. Branching channels have wide application in many practical projects, such as irrigation and drainage network systems, water and waste water treatment plants, and many water resources projects. In the last decades, extensive theoretical and experimental investigations of the branching open channels have been carried out to understand the characteristics of this branching flow, varying from case studies to theoretical and experimental investigations. The objectives of this paper are to review and summarise the relevant literatures regarding branching channel flow. These literatures were reviewed based on flow characteristics, physical characteristics, and modeling of the branching flow. Investigations of the flow into branching channel show that the branching discharge depends on many interlinked parameters. It increases with the decreasing of the main channel flow velocity and Froude number at the upstream of the branch channel junction. Also it increases with the increasing of the branch channel bed slope. In subcritical flow, water depth in the branch channel is always lower than the main channel water depth. The flow diversion to the branch channel leads to an increase of water depth at the downstream of the main channel. From the review, it is important to highlight that most of the study concentrated on flow characteristics in a right angle branch channel with a rigid boundary. Investigations on different branching angles with movable bed have still to be explored.