xvi CONTENTS 12.7 A Value Engineering Approach to the Use of Composite Materials 466 12.8 Conclusion 474 References 474 Chapter 13 Airworthiness Considerations For Airframe Structures 477 13.1 Overview 477 13.2 Certification of Airframe Structures 480 13.3 The Development of Design Allowables 482 13.4 Demonstration of Static Strength 484 13.5 Demonstration of Fatigue Strength 486 13.6 Demonstration of Damage Tolerance 487 13.7 Assessment of the Impact Damage Threat 487 References 488 Chapter 14 Three-Dimensionally Reinforced Preforms and Composites 491 14.1 Introduction 491 14.2 Stitching 492 14.3 Z-Pinning 498 14.4 Three-Dimensional Weaving 502 14.5 Braiding 507 14.6 Knitting 515 14.7 Non-crimp Fabrics 519 14.8 Conclusion 523 References 523 Chapter 15 Smart Structures 525 15.1 Introduction 525 15.2 Engineering Approaches 526 15.3 Selected Applications and Demonstrators 531 15.4 Key Technology Needs 544 References 545 Chapter 16 Knowledge-Based Engineering,Computer-Aided Design,and Finite Element Analysis 549 16.1 Knowledge-Based Design Systems 549 16.2 Finite Element Modelling of Composite Structures 552 16.3 Finite Element Solution Process 553 16.4 Element Types 562 16.5 Finite Element Modelling of Composite Structures 563 16.6 Implementation 566 16.7 Design Optimization 568 References 569
xvi CONTENTS 12.7 A Value Engineering Approach to the Use of Composite Materials 12.8 Conclusion References Chapter 13 Airworthiness Considerations For Airframe Structures 13.1 Overview 13.2 Certification of Airframe Structures 13.3 The Development of Design Allowables 13.4 Demonstration of Static Strength 13.5 Demonstration of Fatigue Strength 13.6 Demonstration of Damage Tolerance 13.7 Assessment of the Impact Damage Threat References Chapter 14 Three-Dimensionally Reinforced Preforms and Composites 14.1 Introduction 14.2 Stitching 14.3 Z-Pinning 14.4 Three-Dimensional Weaving 14.5 Braiding 14.6 Knitting 14.7 Non-crimp Fabrics 14.8 Conclusion References Chapter 15 Smart Structures 15.1 15.2 15.3 15.4 Chapter 16 Introduction Engineering Approaches Selected Applications and Demonstrators Key Technology Needs References Knowledge-Based Engineering, Computer-Aided Design, and Finite Element Analysis 16.1 Knowledge-Based Design Systems 16.2 Finite Element Modelling of Composite Structures 16.3 Finite Element Solution Process 16.4 Element Types 16.5 Finite Element Modelling of Composite Structures 16.6 Implementation 16.7 Design Optimization References 466 474 474 477 477 480 482 484 486 487 487 488 491 491 492 498 502 507 515 519 523 523 525 525 526 531 544 545 549 549 552 553 562 563 566 568 569
CONTENTS xvii Appendix Overview of Some Sensors and Actuators Used for Smart Structure Applications 571 A.1 Piezoelectric Materials 571 A.2 Shape Memory Alloys 573 A.3 Optical Fiber Sensors 574 A.4 Electrorheological Fluids 577 A.5 Magnetostrictive Materials 577 A.6 Micro-Electro-Mechanical Systems 577 A.7 Comparison Of Actuators 578 References 579 Index 581
CONTENTS Appendix Overview of Some Sensors and Actuators Used for Smart Structure Applications A. 1 Piezoelectric Materials A.2 Shape Memory Alloys A.3 Optical Fiber Sensors A.4 Electrorheological Fluids A.5 Magnetostrictive Materials A.6 Micro-Electro-Mechanical Systems A.7 Comparison Of Actuators References Index
1 Introduction and Overview 1.1 General Since the first edition of this textbook'in 1986,the use of high-performance polymer-matrix fiber composites in aircraft structures has grown steadily, although not as dramatically as predicted at that time.This is despite the significant weight-saving and other advantages that these composites can provide. The main reason for the slower-than-anticipated take-up is the high cost of aircraft components made of composites compared with similar structures made from metal,mainly aluminum,alloys.Other factors include the high cost of certification of new components and their relatively low resistance to mechanical damage,low through-thickness strength,and (compared with titanium alloys) temperature limitations.Thus,metals will continue to be favored for many airframe applications. The most important polymer-matrix fiber material and the main subject of this and the previous book,Composite Materials for Aircraft Structures,is carbon fiber-reinforced epoxy(carbon/epoxy).Although the raw material costs of this and similar composites will continue to be relatively high,with continuing developments in materials,design,and manufacturing technology,their advantages over metals are increasing. However,competition will be fierce with continuing developments in structural metals.In aluminum alloys developments include improved toughness and corrosion resistance in conventional alloys;new lightweight alloys(such as aluminum lithium);low-cost aerospace-grade castings;mechanical alloying (high-temperature alloys);and super-plastic forming.For titanium,they include use of powder preforms,casting,and super-plastic-forming/diffusion bonding. Advanced joining techniques such as laser and friction welding,automated riveting techniques,and high-speed (numerically controlled)machining also make metallic structures more affordable. The growth in the use of composites in the airframes in selected aircraft is illustrated in Figure 1.1.However,despite this growth,the reality is,as illustrated in Figure 1.2 for the U.S.Navy F-18 fighter,that airframes (and engines)will continue to be a mix of materials.These will include composites of various types and a range of metal alloys,the balance depending on structural and economic factors
1 Introduction and Overview 1.1 General Since the first edition of this textbook 1 in 1986, the use of high-performance polymer-matrix fiber composites in aircraft structures has grown steadily, although not as dramatically as predicted at that time. This is despite the significant weight-saving and other advantages that these composites can provide. The main reason for the slower-than-anticipated take-up is the high cost of aircraft components made of composites compared with similar structures made from metal, mainly aluminum, alloys. Other factors include the high cost of certification of new components and their relatively low resistance to mechanical damage, low through-thickness strength, and (compared with titanium alloys) temperature limitations. Thus, metals will continue to be favored for many airframe applications. The most important polymer-matrix fiber material and the main subject of this and the previous book, Composite Materials for Aircraft Structures, is carbon fiber-reinforced epoxy (carbon/epoxy). Although the raw material costs of this and similar composites will continue to be relatively high, with continuing developments in materials, design, and manufacturing technology, their advantages over metals are increasing. However, competition will be fierce with continuing developments in structural metals. In aluminum alloys developments include improved toughness and corrosion resistance in conventional alloys; new lightweight alloys (such as aluminum lithium); low-cost aerospace-grade castings; mechanical alloying (high-temperature alloys); and super-plastic forming. For titanium, they include use of powder preforms, casting, and super-plastic-forming/diffusion bonding. Advanced joining techniques such as laser and friction welding, automated riveting techniques, and high-speed (numerically controlled) machining also make metallic structures more affordable. The growth in the use of composites in the airframes in selected aircraft is illustrated in Figure 1.1. However, despite this growth, the reality is, as illustrated in Figure 1.2 for the U.S. Navy F-18 fighter, that airframes (and engines) will continue to be a mix of materials. These will include composites of various types and a range of metal alloys, the balance depending on structural and economic factors
2 COMPOSITE MATERIALS FOR AIRCRAFT STRUCTURES eungonns 4053025 JSF◆ B2 V-22,年-22 0 AV8B Rafale 15 F-18E/F Q A320 ◆ 6330 F-18A 5 ◆ A340 0 F-15AF-16A767737 MD11 C17A 1970 1980 1990 2000 2010 Approximate Year of Introduction Fig.1.1 Growth of use of advanced composites in airframe structures. In this introductory chapter,the incentives or drivers for developing improved materials for aircraft applications are discussed.This is followed by a brief overview of fiber composites,including polymer,metal,and ceramic-matrix composites as well as hybrid metal/composite laminates.Other than polymer- matrix composites,these composites are not considered elsewhere in this book and so are discussed in this chapter for completeness. PERCENT OF STRUCTURAL WEIGHT F/A-F/A- 18C/D 18E/F Aluminum 49 31 Steel 尔 14 Titanium 13 24 Carbon Eposy 10 19 Other 3 的 100 100 Fig.1.2 Schematic diagram of fighter aircraft F-18 E/F.For comparison details of the structure of the earlier C/D model are also provided in the inset table
2 COMPOSITE MATERIALS FOR AIRCRAFT STRUCTURES 40 E X e < 35 30 25 20 15 10 5 0 1970 AV8B F-18A • •• F-15~ F-16A 767 A320 B2 t 737 V-22 4~.22 Rafale F-18E/F A~0 ~77 MD11 C17A JSF-O 1980 1990 2000 2010 Approximate Year of Introduction Fig. 1.1 Growth of use of advanced composites in airframe structures. In this introductory chapter, the incentives or drivers for developing improved materials for aircraft applications are discussed. This is followed by a brief overview of fiber composites, including polymer, metal, and ceramic-matrix composites as well as hybrid metal/composite laminates. Other than polymermatrix composites, these composites are not considered elsewhere in this book and so are discussed in this chapter for completeness. PERCENT OF STRUCTURAL WEIGHT ~ Aluminum I Steel IB Titanium I Carbon Ep Other F/A- F/A- 18C/D 18E/F An 11 Fig. 1.2 Schematic diagram of fighter aircraft F-18 E/F. For comparison details of the structure of the earlier C/D model are also provided in the inset table
INTRODUCTION AND OVERVIEW 3 1.2 Drivers for Improved Airframe Materlals Weight saving through increased specific strength or stiffness is a major driver for the development of materials for airframes.2 However,as listed in Table 1.1,there are many other incentives for the introduction of a new material. A crucial issue in changing to a new material,even when there are clear performance benefits such as weight saving to be gained,is affordability.This includes procurement (up front)cost(currently the main criterion)and through- life support cost(i.e.,cost of ownership,including maintenance and repair).Thus the benefits of weight savings must be balanced against the cost.Approximate values that may be placed on saving 1 kilogram of weight on a range of aircraft types are listed in Table 1.2. In choosing new materials for airframe applications,it is essential to ensure that there are no compromises in the levels of safety achievable with con- ventional alloys.Retention of high levels of residual strength in the presence of typical damage for the particular material (damage tolerance)is a critical issue. Durability,the resistance to cyclic stress or environmental degradation and damage,through the service life is also a major factor in determining through-life support costs.The rate of damage growth and tolerance to damage determine the frequency and cost of inspections and the need for repairs throughout the life of the structure. 1.3 High-Performance Fiber Composite Concepts The fiber composite approach can provide significant improvements in specific(property/density)strength and stiffness over conventional metal alloys. As summarized in Table 1.3,the approach is to use strong,stiff fibers to reinforce a relatively weaker,less stiff matrix.Both the fiber and matrix can be a polymer,a metal,or a ceramic. Table 1.1 Drivers for Improved Material for Aerospace Applications ·Weight Reduction Improved Performance -increased range -smoother,more aerodynamic form -reduced fuel cost -special aeroelastic properties -higher pay load -increased temperature capability -increased maneuverability -improved damage tolerance .Reduced Acquisition Cost -reduced detectability -reduced fabrication cost Reduced Through-Life Support Cost -improved“"Hy-to-buy”ratio resistance to fatigue and corrosion -reduced assembly costs -resistance to mechanical damage
INTRODUCTION AND OVERVIEW 3 1.2 Drivers for Improved Airframe Materials Weight saving through increased specific strength or stiffness is a major driver for the development of materials for airframes. 2 However, as listed in Table 1.1, there are many other incentives for the introduction of a new material. A crucial issue in changing to a new material, even when there are clear performance benefits such as weight saving to be gained, is affordability. This includes procurement (up front) cost (currently the main criterion) and throughlife support cost (i.e., cost of ownership, including maintenance and repair). Thus the benefits of weight savings must be balanced against the cost. Approximate values that may be placed on saving 1 kilogram of weight on a range of aircraft types are listed in Table 1.2. In choosing new materials for airframe applications, it is essential to ensure that there are no compromises in the levels of safety achievable with conventional alloys. Retention of high levels of residual strength in the presence of typical damage for the particular material (damage tolerance) is a critical issue. Durability, the resistance to cyclic stress or environmental degradation and damage, through the service life is also a major factor in determining through-life support costs. The rate of damage growth and tolerance to damage determine the frequency and cost of inspections and the need for repairs throughout the life of the structure. 1.3 High-Performance Fiber Composite Concepts The fiber composite approach can provide significant improvements in specific (property/density) strength and stiffness over conventional metal alloys. As summarized in Table 1.3, the approach is to use strong, stiff fibers to reinforce a relatively weaker, less stiff matrix. Both the fiber and matrix can be a polymer, a metal, or a ceramic. Table 1.1 Drivers for Improved Material for Aerospace Applications • Weight Reduction • Improved Performance - increased range - smoother, more aerodynamic form - reduced fuel cost - special aeroelastic properties - higher pay load - increased temperature capability - increased maneuverability - improved damage tolerance • Reduced Acquisition Cost - reduced detectability - reduced fabrication cost • Reduced Through-Life Support Cost - improved "fly-to-buy" ratio - resistance to fatigue and corrosion - reduced assembly costs - resistance to mechanical damage