Probability, Reliability and Statistical Methods in Engineering Design

The problem of impact damage in laminated composite structures, and the consequent reduction in residual strength, has been a topic of continual research for over two decades. The number of journal papers on the subject now runs into four figures and most have been conscientiously reviewed by Abrate(1991, 1994, 1998). This review is not intended to be in the academic tradition, with emphasis on acknowledging the authorship of all the various research initiatives. Instead we present our opinions so that the reader can appreciate our current understanding of the problem, our capability of predicting by analysis, and the scope of the design tools for avoiding structural damage, or at least designing damage tolerant aerospace structures.

Impact on composite structures

The path towards delamination-free drilling of composite materials

Compressive failure of composites, part I: Testing and micromechanical theories

The invention relates to a wind turbine blade with at least one control surface and an actuator inside the main body of the wind turbine blade for moving the control surface, wherein the actuator comprises a fluidic muscle, a controller and a pump, and wherein the fluidic muscle is adapted to change in length and width when the pressure of the fluid within the fluidic muscle is varied.

Wind turbine blade

The influence of different parameters on the impact behavior of laminated composite plates is considered analytically. A Rayleigh-Ritz energy method was used to spatially discretize the time-varying boundary value problem and a set of coupled, ordinary differential equations in time were obtained based on the discretized system Lagrangian. The effects of shearing deformation, bending-twisting coupling, and nonlinear contact behavior were included in the model. The resulting equations were integrated using the implicit Newmark beta method without the effects of rotary inertia. The results indicate that the effective mass of the plate is often an important effect in the response to impact events. In general, the influence of the constitutive behavior dominates for very low velocity impact, whereas the target mass properties become more important as the impactor velocity increases. This importance of mass clearly shows that impactor kinetic energy is not sufficient to characterize the impactor as the impactor mass is shown to have a large influence on the resulting dynamic behavior. In addition to these parameters, the effects of preload and material properties are considered and discussed.

Transient response of graphite/epoxy and Kevlar/epoxy laminates subjected to impact

This report presents the major findings of the Montana State University Composite Materials Fatigue Program from 1997 to 2001, and is intended to be used in conjunction with the DOE/MSU Composite Materials Fatigue Database. Additions of greatest interest to the database in this time period include environmental and time under load effects for various resin systems; large tow carbon fiber laminates and glass/carbon hybrids; new reinforcement architectures varying from large strands to prepreg with well-dispersed fibers; spectrum loading and cumulative damage laws; giga-cycle testing of strands; tough resins for improved structural integrity; static and fatigue data for interply delamination; and design knockdown factors due to flaws and structural details as well as time under load and environmental conditions. The origins of a transition to increased tensile fatigue sensitivity with increasing fiber content are explored in detail for typical stranded reinforcing fabrics. The second focus of the report is on structural details which are prone to delamination failure, including ply terminations, skin-stiffener intersections, and sandwich panel terminations. Finite element based methodologies for predicting delamination initiation and growth in structural details are developed and validated, and simplified design recommendations are presented.

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Fatigue of Composite Materials and Substructures for Wind Turbine Blades

Thick composite plates subjected to lateral loading

A fiberglass blade was designed for the Atlantic Orient Corporation (AOC) H/50 wind turbine through the use of finite element (FE) modeling techniques. In this initial design phase, the goals were: 1) make the blade as stiff as the previously designed laminated wood blade, 2) minimize resonant operating conditions, 3) design the blade to withstand extreme wind conditions, and 4) make the blade compatible with reasonable manufacturing techniques. The modeling assumptions used are discussed and the final results, for this initial design phase, are presented. Based on the J?E model, the designed blade will be able to withstand extreme wind conditions through elastic deformation, and resonant operating conditions will be minimized. This document is an overview of the design and manufacturing synthesis data of composite wind turbine blades for applications to the Sandia National Laboratories’ NuMAD wind turbine blade design tool.

Analysis of a Composite Blade Design for the AOC 15/50 Wind Turbine using a Finite Element Model

An approach is formulated to treat the behavior of composites subjected to impact as the sequential effect of a number of events. The sequence for the analysis of im pact presented here is as follows. First, a global analysis of impact of the structure is con ducted. In this study, a plate is analyzed in a time marching scheme to properly account for nonlinearities during the impact event. This provides loads introduced into the struc ture during impact. These loads are then introduced into a local deformation and strain re sponse model just below the impactor to refine the analysis in the local region where damage occurs. Damage is predicted in the laminate on a ply-by-ply basis. Excellent agreement between the models and test data taken during the impact event is found. This is denoted as the Damage Resistance portion of the problem. Given the pre-existing damage, an analysis of the damaged structure is conducted. This entails using an average strain criterion for fiber-dominated fracture around the dam...

Douglas S. Cairns

Papers

Transient response of graphite/epoxy and Kevlar/epoxy laminates subjected to impact

Fatigue of Composite Materials and Substructures for Wind Turbine Blades

Thick composite plates subjected to lateral loading

Analysis of a Composite Blade Design for the AOC 15/50 Wind Turbine using a Finite Element Model

A Consistent Engineering Methodology for the Treatment of Impact in Composite Materials