Bending-induced local buckling during offshore installation of multi-layered FRP pipelines

In the last two decades FRP pipelines have attracted the attention of the oil industry because of their high strength, excellent fatigue performance and low specific weight. On the other hand, the final cost of installation of FRP pipelines is comparable to the cost of carbon steel ones. Therefore, their implementation in offshore applications seems to be advantageous. During offshore installation, the curvatures of the pipes during the S-lay or J-lay installation processes cause high bending stresses and risk for bending-induced local buckling. Since the pipe wall is multi-layered and the laminae are anisotropic, the calculation of critical bending moments is difficult. In the present work, an analytical solution of critical bending moments for bending-induced local buckling is provided. The proposed method uses the classical lamination theory of multi-layered anisotropic materials and Flügge’s assumption for local buckling analysis of pipelines. Results for E-Glass fiber reinforced polymeric pipelines are provided and discussed.

Design Optimization of Composite Lay-up Sequence and Orientation to Achieve Minimum Weight for Racing Seat

Composites have proved their usefulness in the automotive industry during recent years. Many automobile companies use them in different parts to reduce weight without hampering strength. In a composite material, Lay-up sequence and orientation highly affects the properties of the laminate. Therefore, it is important to perform design optimization on a component to achieve high strength in minimum weight. This paper deals with the optimization of lay-up for composite Racing Seat using finite element analysis. Different lay-up sequences for laminates including, cross-ply [0/90]n, angle-ply [±α]n, and [0/90/±α]n are analysed. The lay-up sequence, orientation and ply number are optimized using composite material carbon fibre/Epoxy. Driver’s ergonomics and impact sustainability are considered constraints for weight optimization. Driver’s ergonomics were based on 95th percentile male and 5th percentile female rule. Force analysis is performed on the seat according to SFI 39.2 to evaluate the strength requirement. Finite element analysis of composite racing seat is performed via commercial finite element code ANSYS and using the capabilities of ANSYS Composite PrepPost (ACP) to form desired composite lay-up. A finite element code is based on classical lamination theory; including Puck’s failure criterion for first-ply failure. The seat is divided into three portions with a different number of layers considering the values and specific nature of acting forces; which resulted in different thicknesses in different regions. The optimization results show that for all the angles of Angle-ply laminate considered, Angle-ply laminates with an angle of 45⁰ provides a more optimum design. The minimum weight obtained is 10.15 kg.

A Plane-Stress Damage Model for Vectran Laminated Composite

The aim of this paper is to present a plane-stress damage model based on the Classical Lamination Theory (CLT), developed for polymer fibre-based composite. The proposed numerical model utilises a damage mechanics methodology coupled with fracture mechanics to predict composite failure, particularly under quasi-static and dynamic loadings. In addition, the proposed constitutive equations consider a single secant modulus to describe its tensile and compressive modulus, as opposed to the physically-proposed tier models for polymer fibres which possesses a ‘skin–core’ structure. The result of single element and coupon-level modelling showed excellent correlation with the experimental results. It is expected that the proposed numerical model will be able to predict, up to a considerable accuracy, the response of the composite under low and high velocity impact loadings.

Defining relationships between geometry and behavior of bistable composite laminates

Bistability is exhibited by an object when it can be resting in two stable equilibrium states. Certain composite laminates exhibit bistability by having two stable curvatures of opposite sign with the two axes of curvature perpendicular to each other. These laminates can be actuated from one state to the other. The actuation from the original post-cure shape to the second shape is called as ‘snap-through’ and the reverse actuation is called as ‘snap-back’. This phenomenon can be used in applications for morphing structures, energy harvesting, and other applications where there is a conflicting requirement of a structure that is load-carrying, light, and shape-adaptable. MW Hyer first reported this phenomenon in his paper in 1981. He found that thin unsymmetric laminates do not behave according to the predictions of the Classical Lamination Theory (CLT). The CLT is a linear theory and predicts the post-cure shape of thin unsymmetric laminates to be a saddle. MW Hyer developed a non-linear method called the “Extended Classical Lamination Theory” which accurately predicted the laminate to have two cylindrical shapes. Since then, a number of researchers have tried to identify the key parameters affecting the behavior of such laminates. Geometric parameters such as stacking sequence, fibre orientation, cure cycle, boundary conditions, and force of actuation, have all been studied. The objective of this research is to define a relation between the length, width and thickness of square and rectangular laminates required to achieve bistability. Using these relations, a 36 in × 36 in bistable laminate is fabricated with a thickness of 30 CFRP layers. Also, it is proved that a laminate does not lose bistability with an increase in aspect ratio, as long as both sides of the rectangular laminate are above a certain ‘critical length’. A bistable laminate with dimensions of 2 in × 50 in is fabricated. Further, for laminates that are bistable, it is necessary to be able to predict the curvature and force required for actuation. Therefore, a method is developed which allows us to predict the curvature of both stable shapes, as well as the force of actuation of laminates for which the thickness and dimensions are known. Finite Element Analysis is used to carry out the numerical calculations, which are validated by fabricating laminates. The curvature of these laminates is measured using a profilometer and the force of actuation is recorded using a universal test set-up.

Measuring fibre orientation and predicting elastic properties of discontinuous long fibre thermoplastic composites

Elastic properties in critical areas of 3 D shells made from discontinuous long fibre (DLF) composites are difficult to determine via traditional methods, due to the heterogeneity of the material and the geometry of the part. In this paper, a method is proposed to predict the local modulus of DLF composites based on a micrograph of the polished edge of a specimen. The position and orientation of each fibre are extracted from the micrograph and used in conjunction with classical lamination theory to predict the elastic modulus. Fibre discontinuity is accounted for by including a correction factor based on the Cox formula for averaged elastic constants. Model predictions successfully matched the experimental tests results. In a previous study, material flow during compression moulding of recycled DLF panels led to anisotropic behaviour, which was hypothesized to be caused by chip alignment in the flow direction. By using the proposed method, chip alignment due to flow was confirmed and the anisotropy in the elastic modulus was accurately predicted.