《纺织复合材料》课程参考文献（Principles of the Manufacturing of Composite Materials）CHAPTER 1 Introduction

Heat Source From spool Tape Guide rail Mandrel Consolidation roller Heat and pressure FIGURE 1.6(b)Schematic of the thermoplastic composite placement process. FIGURE 1.6(c)A fiber placement machine (courtesy of Aerospace Manufacturing Technology Center,National Research Council of Canada). 12

12 FIGURE 1.6(b) Schematic of the thermoplastic composite placement process. FIGURE 1.6(c) A fiber placement machine (courtesy of Aerospace Manufacturing Technology Center, National Research Council of Canada)

General Characteristics of Manufacturing Using Composites 13 A few specific features can be extracted from the above components and the different manufacturing techniques used to fabricate them. Normally structural components can be classified according to their shape,and the manufacturing technique used depends significantly on the shape of the component as follows: Relatively thin flat plate or shallow shell with free edges. Normally aerospace components have these types of shapes. These are usually made using the hand-lay-up method.The autoclave is the common tool used for making aerospace composite components having these shapes. Components of revolution,such as cylindrical or spherical pressure vessels and pipes.These structures usually have no free edges (except for the end openings).These are usually made using the filament winding method. Components having constant cross section such as tubes,rods,or even components with complex but constant cross section along the length such as door frames.These are usually made using the pultrusion method. Components having complex 3-D configurations.These can be thick or thin.These are usually made using the liquid composite molding (LCM)method. Large structures such as boat hulls,wind turbine blades etc. These are made using a modified form of LCM such as vacuum-assisted LCM.A special process called SCRIMP (seaman composite resin infusion molding process)is usually used to make boat hulls Small and large components,either without free edges or with free edges.These can be made by the fiber placement method. These machines are versatile but require a large amount of capital investment (on the order of several millions of dollars). 2.GENERAL CHARACTERISTICS OF MANUFACTURING USING COMPOSITES Generally,manufacturing using composites involves the processing of two main ingredient materials to make a final product.The ingredients involve the matrix and fiber materials.This processing requires the following: Good bonding between matrix and fibers

A few specific features can be extracted from the above components and the different manufacturing techniques used to fabricate them. Normally structural components can be classified according to their shape, and the manufacturing technique used depends significantly on the shape of the component as follows: • Relatively thin flat plate or shallow shell with free edges. Normally aerospace components have these types of shapes. These are usually made using the hand-lay-up method. The autoclave is the common tool used for making aerospace composite components having these shapes. • Components of revolution, such as cylindrical or spherical pressure vessels and pipes. These structures usually have no free edges (except for the end openings). These are usually made using the filament winding method. • Components having constant cross section such as tubes, rods, or even components with complex but constant cross section along the length such as door frames. These are usually made using the pultrusion method. • Components having complex 3-D configurations. These can be thick or thin. These are usually made using the liquid composite molding (LCM) method. • Large structures such as boat hulls, wind turbine blades etc. These are made using a modified form of LCM such as vacuum-assisted LCM. A special process called SCRIMP (seaman composite resin infusion molding process) is usually used to make boat hulls. • Small and large components, either without free edges or with free edges. These can be made by the fiber placement method. These machines are versatile but require a large amount of capital investment (on the order of several millions of dollars). 2. GENERAL CHARACTERISTICS OF MANUFACTURING USING COMPOSITES Generally, manufacturing using composites involves the processing of two main ingredient materials to make a final product. The ingredients involve the matrix and fiber materials. This processing requires the following: • Good bonding between matrix and fibers General Characteristics of Manufacturing Using Composites 13

14 INTRODUCTION Proper orientation of the fibers Good amount of volume fraction of fibers Uniform distribution of fibers within the matrix material Proper curing or solidification of the resin Limited amount of voids and defects Good dimensional control for the final part The implications of the above are as follows. Good bonding between matrix and fibers.To provide reinforcement so that properties such as strength and stiffness can be enhanced,the fibers need to be bonded to the matrix.If at a certain location,the fibers are not properly bonded to the matrix,dry spots will occur.At this location,there is no proper shear transfer of load between fiber and matrix and the dom- ino effect (as will be discussed in Section 3.1 of this chapter)will occur. These locations will also serve as nuclei for cracks to form.However, there are situations,such as the requirement to absorb impact energy, where partial dry spots may enhance the energy absorbing capability of the composite. Proper orientation ofthe fibers.Proper orientation of the fibers is im- portant since properties such as stiffness and strength are very sensitive to fiber orientation.If the fiber orientation deviates by about 10 from the 0 direction,the stiffness can drop by more than 30%.Fiber orienta- tion may be deviated from the intended orientation due to improper po- sition of the layer during the lay-up step,or due to the flow of liquid resin that pushes the fibers during the filling period in liquid composite molding. Good amount of volume fraction of fibers.In composite materials,the fibers provide stiffness and strength.Therefore the greater the amount of fibers,the better will be these properties.The amount of fibers is usually expressed in terms of volume fraction,v,which is defined as: Vi= (1.1) where V,is volume of fibers and V is volume of the composite material. Properties such as stiffness of a unidirectional composite along the ax- ial direction is given by the rule of mixtures: E。=E,vj+vmEm (1.2)

• Proper orientation of the fibers • Good amount of volume fraction of fibers • Uniform distribution of fibers within the matrix material • Proper curing or solidification of the resin • Limited amount of voids and defects • Good dimensional control for the final part The implications of the above are as follows. Good bonding between matrix and fibers. To provide reinforcement so that properties such as strength and stiffness can be enhanced, the fibers need to be bonded to the matrix. If at a certain location, the fibers are not properly bonded to the matrix, dry spots will occur. At this location, there is no proper shear transfer of load between fiber and matrix and the dom￾ino effect (as will be discussed in Section 3.1 of this chapter) will occur. These locations will also serve as nuclei for cracks to form. However, there are situations, such as the requirement to absorb impact energy, where partial dry spots may enhance the energy absorbing capability of the composite. Proper orientation of the fibers. Proper orientation of the fibers is im￾portant since properties such as stiffness and strength are very sensitive to fiber orientation. If the fiber orientation deviates by about 10° from the 0° direction, the stiffness can drop by more than 30%. Fiber orienta￾tion may be deviated from the intended orientation due to improper po￾sition of the layer during the lay-up step, or due to the flow of liquid resin that pushes the fibers during the filling period in liquid composite molding. Good amount of volume fraction of fibers. In composite materials, the fibers provide stiffness and strength. Therefore the greater the amount of fibers, the better will be these properties. The amount of fibers is usually expressed in terms of volume fraction, vf which is defined as: v V V f f c = (1.1) whereVf is volume of fibers and Vc is volume of the composite material. Properties such as stiffness of a unidirectional composite along the ax￾ial direction is given by the rule of mixtures: E Ev vE c = + f f m m (1.2) 14 INTRODUCTION

General Characteristics of Manufacturing Using Composites 15 Where subscript frefers to fiber,and m refers to matrix. The fiber volume fraction and matrix volume fraction are related by: 1=v+vm+vv (1.3) Where the last term refers to volume fraction of voids. For good quality composites,the amount of voids should be minimum (less than 1%)and Equation (1.3)can be approximated to be 1=v+Vm (1.4) Using Equation (1.4)in Equation (1.2),the modulus is expressed as: E。=(E,-Em)Pr+Em (1.5) The modulus is linearly proportional to the fiber volume fraction. Therefore the larger the fiber volume fraction,the better the mechanical properties.It should be noted,however that the fiber volume fraction cannot be 1 because this would mean that there is no matrix material which,in turn,would mean dry bundles of fibers and the domino effect as mentioned in Section 3.1 will prevail. Uniform distribution of fibers within the matrix material.Figure 1.14 shows a cross section of a unidirectional composite layer.The white dots show the cross section of the fibers and the dark area represents the ma- trix.One can see that at the fine scale,the distribution of the fibers is uni- form in some region but not in other regions.The region where there is more matrix than fiber is called a resin rich area.It is not a good idea to have large or many resin rich regions because there will also be weak ar- eas.Under loading,these areas can serve as locations for crack to nucle- ate. Proper curing of the resin.In the manufacturing of polymer matrix composites,the resin first occurs in the form of low viscosity liquid so that it can flow and wet the surface of the fibers.After wetting has been completed,the resin needs to solidify and harden.For thermoset resin, this is called curing;and for thermoplastic resin,this is called solidifica-

Where subscript f refers to fiber, and m refers to matrix. The fiber volume fraction and matrix volume fraction are related by: 1=++ vvv f m v (1.3) Where the last term refers to volume fraction of voids. For good quality composites, the amount of voids should be minimum (less than 1%) and Equation (1.3) can be approximated to be 1= + v v f m (1.4) Using Equation (1.4) in Equation (1.2), the modulus is expressed as: E E Ev E c =− + f m f m ( ) (1.5) The modulus is linearly proportional to the fiber volume fraction. Therefore the larger the fiber volume fraction, the better the mechanical properties. It should be noted, however that the fiber volume fraction cannot be 1 because this would mean that there is no matrix material which, in turn, would mean dry bundles of fibers and the domino effect as mentioned in Section 3.1 will prevail. Uniform distribution of fibers within the matrix material. Figure 1.14 shows a cross section of a unidirectional composite layer. The white dots show the cross section of the fibers and the dark area represents the ma￾trix. One can see that at the fine scale, the distribution of the fibers is uni￾form in some region but not in other regions. The region where there is more matrix than fiber is called a resin rich area. It is not a good idea to have large or many resin rich regions because there will also be weak ar￾eas. Under loading, these areas can serve as locations for crack to nucle￾ate. Proper curing of the resin. In the manufacturing of polymer matrix composites, the resin first occurs in the form of low viscosity liquid so that it can flow and wet the surface of the fibers. After wetting has been completed, the resin needs to solidify and harden. For thermoset resin, this is called curing; and for thermoplastic resin, this is called solidifica￾General Characteristics of Manufacturing Using Composites 15

16 INTRODUCTION tion.In both cases,the resin needs to be hard and stiff for the reinforce- ment effect to take place.If there are regions where the resin is not hard enough,they will be weak and can serve as crack nucleation areas. Limited amount of voids and defects.Voids and defects may be formed during the manufacturing of composites.Voids can arise due to lack of compaction of many layers together,or due to low pressure in the resin during curing.The amount of voids needs to be a minimum to be accept- able.A limit of about 1%is commonly used.Defects such as delamination between layers,cracks,fiber mis-orientation,or nonuni- form fiber distribution may not be acceptable. Good dimensional control for the final part.Polymeric resins shrink when they change from liquid state to solid state.The degree of shrink- age can be between about 5%-8%depending on the type of materials. This shrinkage of the material may cause residual stresses in the part,and also out-of dimensions or warping.For a large structure such as the wing of an aircraft,a few percentages of shrinkage of the material can translate into significant deformation of the structure.Another problem that may occur is the surface finish of parts such as automobile panels which may be adversely affected by this shrinkage.Resins with Low Profile Addi- tives are usually used to control shrinkage. 2.1 Metal versus Composite Manufacturing Manufacturing using composites has differences from manufacturing using metals: In metals such as steel or aluminum,materials with finished form such as rods,slabs,or sheets are available.The making of a finished product such as a car body or the box frame for a computer only requires working on these finished forms. Processes such as cutting,bending,forming,welding,or drilling are used on these finished forms to make the finished product. In composites,the steps that transform the finished form to the final structure are usually bypassed.A manufacturer using composite materials has to work directly from the ingredients of fiber and matrix to make the finished product itself.Figure 1.7(a) shows the different stages of existence of composite constituents up to the final product: -Stage a:At this stage,the materials appear in raw basic form.For fibers,these consist of fiber either in the form of filaments or fi-

tion. In both cases, the resin needs to be hard and stiff for the reinforce￾ment effect to take place. If there are regions where the resin is not hard enough, they will be weak and can serve as crack nucleation areas. Limited amount of voids and defects. Voids and defects may be formed during the manufacturing of composites. Voids can arise due to lack of compaction of many layers together, or due to low pressure in the resin during curing. The amount of voids needs to be a minimum to be accept￾able. A limit of about 1% is commonly used. Defects such as delamination between layers, cracks, fiber mis-orientation, or nonuni￾form fiber distribution may not be acceptable. Good dimensional control for the final part. Polymeric resins shrink when they change from liquid state to solid state. The degree of shrink￾age can be between about 5%–8% depending on the type of materials. This shrinkage of the material may cause residual stresses in the part, and also out-of dimensions or warping. For a large structure such as the wing of an aircraft, a few percentages of shrinkage of the material can translate into significant deformation of the structure. Another problem that may occur is the surface finish of parts such as automobile panels which may be adversely affected by this shrinkage. Resins with Low Profile Addi￾tives are usually used to control shrinkage. 2.1 Metal versus Composite Manufacturing Manufacturing using composites has differences from manufacturing using metals: • In metals such as steel or aluminum, materials with finished form such as rods, slabs, or sheets are available. The making of a finished product such as a car body or the box frame for a computer only requires working on these finished forms. Processes such as cutting, bending, forming, welding, or drilling are used on these finished forms to make the finished product. • In composites, the steps that transform the finished form to the final structure are usually bypassed. A manufacturer using composite materials has to work directly from the ingredients of fiber and matrix to make the finished product itself. Figure 1.7(a) shows the different stages of existence of composite constituents up to the final product: —Stage a: At this stage, the materials appear in raw basic form. For fibers, these consist of fiber either in the form of filaments or fi- 16 INTRODUCTION