Dynamic Deformation, Damage and Fracture in Composite Materials and Structures

Vadim Silberschmidt, Vadim V. Silberschmidt

• Publisher: Woodhead Publishing
• Year: 2016
• Print ISBN: 9780081008706
• eBook ISBN: 9780081000830
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Composite materials, with their higher exposure to dynamic loads, have increasingly been used in aerospace, naval, automotive, sports and other sectors over the last few decades. Dynamic Deformation, Damage and Fracture in Composite Materials and Structures reviews various aspects of dynamic deformation, damage and fracture, mostly in composite laminates and sandwich structures, in a broad range of application fields including aerospace, automotive, defense and sports engineering. As the mechanical behavior and performance of composites varies under different dynamic loading regimes and velocities, the book is divided into sections that examine the different loading regimes and velocities. Part one examine low-velocity loading and part two looks at high-velocity loading. Part three then assesses shock and blast (i.e. contactless) events and the final part focuses on impact (contact) events. As sports applications of composites are linked to a specific subset of dynamic loading regimes, these applications are reviewed in the final part. - Examines dynamic deformation and fracture of composite materials - Covers experimental, analytical and numerical aspects - Addresses important application areas such as aerospace, automotive, wind energy and defence, with a special section on sport applications

1

Introduction

V.V. Silberschmidt     Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, UK

Abstract

In recent years, the extensive use of composites in aerospace, wind energy, transportation, naval and defence systems and structures as well as in sports products increased the need for improved understanding of dynamic deformation, damage and fracture of composites since such components and structures are exposed in service not only to quasi-static loading conditions. This is the main motivation for this book. The introductory chapter provides a brief description of main directions of research into dynamic deformation and fracture of composites and discusses what is covered in the book.

Keywords

Composites; Damage; Dynamic deformation; Fracture; Laminates

 

In recent years, the use of composite materials that has already demonstrated a continuing increase in various industries has undergone another step change linked to their broad introduction into automotive structures, including a start of mass production of a composite-body BMW i3 series in 2013. This development—together with extensive employment of composites in aerospace, wind energy, transportation, naval and defence systems and structures as well as in sports products—exacerbated a need for improved understanding of dynamic deformation, damage and fracture of composites since such components and structures are exposed in service to quasi-static loading conditions, and various types of dynamic loads and regimes expanded significantly. If in the case of aerospace structures, most dynamic events could be related only to a few specific scenarios such as caused by dropped tools, hail, a bird strike or runway debris; an extensive use of composites both in body panels and critical components of cars will broaden significantly their types as well as occurrence.

A mechanics-of-composites community has already accumulated a wealth of knowledge and expertise in this area of research, and this book presents an up-to-date overview of developments and achievements in this challenging area. Inevitably, not everything can be covered in a single volume. Hence, this monograph is limited to laminates, with fibre-reinforced composites in its centre. Two main reasons are behind this choice: a ubiquitous use of these materials and significantly more complex damage and failure scenarios compared to those in particulate composites. Sandwich structures are a natural extension, since they have many common features with laminates and in many cases use the latter as their face/back sheets. Thus, the book covers carbon- and glass-fibre-reinforced polymer-matrix composites (including fabric reinforced), hybrid composites, various sandwich structures and fibre–metal laminates. The effect of microstructural enhancement, for instance, by introduction of additional layers, nanoscale reinforcement etc. on dynamic performance and properties is also discussed.

A transition from quasi-static loading regimes to dynamic ones in heterogeneous materials is much more complex than in traditional structural materials such as metals and alloys. A presence of phases with various mechanical properties and interfaces affects the character of stress-wave propagation, resulting in complex spatiotemporal scenarios of damage and failure evolution, initiated in multiple spots. The damage processes in dynamically loaded composites are also multi-mode, governed by various mechanisms and, hence, requesting different models and assessment tools. Importantly, a loading rate plays not merely a parametric part in realisation of dynamic deformation and failure of composites. Its increase is accompanied by a significant change in a character of evolution of various damage modes, their interaction and prominence. Very high loading speeds can even result in a change of a state of constitutive materials. Hence, the book follows a well-established tradition to differentiate between low-, high- and hyper-velocity regimes, with each covered either separately or in juxtaposition with each other. The structure of the book also reflects differences between blast and impact events, evident in variation of damage-initiation and damage-propagation processes. Blasts both in air and in water are discussed, since they are related to different application conditions.

The book contains also contributions related to dynamic deformation and fracture of composites in sports products. Though composites have been used in such products for decades, and, in general, in terms of global consumption, e.g. of carbon fibres, sports and leisure is behind only wind energy and aerospace/defence, they are significantly less researched.

In this book, world-leading experts cover various aspects of deformation behavior, damage and fracture of composites under dynamic loading conditions, using experimental, analytical and numerical approaches. A starting point for many studies is analysis of damage in composites under quasi-static loading conditions. This is a rather natural step, since it provides a reference point for assessment of dynamic damage and fracture processes. A vivid difference in their realisation is a strong justification for research focused on dynamic behaviour.

To quantify this difference, mechanical tests and microstructural characterisation of damage are broadly used. The former are performed to establish mechanical properties in an undamaged (virginal) state of composites at various loading rates as well as to evaluate the effect of damage on properties and performance after impacts or other dynamic events. Importantly, in many cases it is impossible to obtain dynamic material properties directly; rather, a process of transient interaction between a specimen and a loading system should be studied to assess the respective strain-rate behaviour. The methods of microstructural characterisation are employed to characterise distribution of constituents and to study the extent of damage, using various schemes. In many cases they need a painstaking analysis of different inter- and intra-ply modes of damage at various locations in composites. Many material systems of laminates are opaque, preventing direct visual observation of sub-surface defects. In addition, simultaneous realisation of delamination at various interfaces through thickness of composites limits applicability of 2D schemes such as C-scans, while high-resolution 3D methods such as computed tomography provide detailed data for relatively small volumes. All of these factors additionally complicate acquisition of quantitative data on damage. Hence, there is a strong demand for predictive tools, capable to reproduce adequately the evolution of dynamic damage modes in time and space.

Some analytic approaches, presented in the book, provide important ways to assess various failure mechanisms and processes. Inevitably, because of complexity of spatiotemporal features of damage in multi-material systems with complex microstructures and in presence of many interfaces, such schemes are limited either to single damage mechanisms (e.g. delamination) or based on some assumptions that cannot be easily expanded to other cases. As a result, advanced numerical schemes (usually, finite elements) have become inescapable in analysis of dynamic deformation and fracture of composites and are properly presented in this volume. These approaches are still in development due to complexity of implementation of the effects of transient loads (with multi-body interaction and stress waves, in many cases) at various time and length scales in systems with boundaries and connectivity changing during modelled events. Field-coupling also presupposes a transition to multi-physics formulation, requiring even more efforts for determining of respective material parameters.

From experimental observations it is well known that loading, fixture and contact conditions can change significantly damage scenarios even in the same materials. Additionally, an increase in loading velocity for the same combination of a target and projectile shifts a balance in interaction of global and local mechanical processes to more spatially localised ones. All these factors (together with many others) have found their reflection in the chapters of this book.

Inevitably, apart from general contribution to mechanics of composite materials, many topics in the volume are motivated by various applications of laminates and sandwich structures. As a result, damage-tolerant design and respective definitions are discussed to provide foundation for suggestion of new structures and components. Many case studies cover various aspects of dynamic deformation and damage, from the effect of varying loading conditions (e.g. impacts and blasts of different intensity and duration) to the influence of layout and shape of laminate specimens as well as of microstructural features.

The book provides a comprehensive overview of the state-of-the-art testing, analysis and simulations of most common types of layered composite materials exposed to application-relevant dynamic loading conditions.

Part One

Low-velocity loading

Outline

2. Damage tolerance of composite structures under low-velocity impact

3. Damage in laminates from low-velocity impacts

4. Multiscale modeling of delamination damage in laminated structures

5. Low-velocity impact of composite laminates: damage evolution

6. Low-velocity impact on laminates

2

Damage tolerance of composite structures under low-velocity impact

C. Bouvet, and S. Rivallant Université de Toulouse, CNRS, ISAE-Supaéro, Institut Clément Ader, Toulouse, France

Abstract

Low-velocity impact is one of the most critical load factors for composite laminates. Indeed, for structures submitted to low-energy impacts or small-object drops, such as tools during assembly or maintenance operations, composite laminates reveal a brittle behavior and can undergo significant damage in terms of matrix cracks, fiber breakage, or delamination. This damage is particularly dangerous because it drastically reduces the residual mechanical characteristics of the structure, and at the same time can leave very limited visible marks on the ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Related titles
• Copyright
• List of contributors
• Woodhead Publishing Series in Composites Science and Engineering
• 1. Introduction
• Part One. Low-velocity loading
• Part Two. High-velocity loading
• Part Three. Shock and blast
• Part Four. Impact and penetration
• Part Five. Sports applications
• Index