MIL-HDBK-17-3F Volume 3,Chapter 2 Materials and Processes-The Effects of Variability on Composite Properties CHAPTER 2 MATERIALS AND PROCESSES-THE EFFECTS OF VARIABILITY ON COMPOSITE PROPERTIES 2.1 INTRODUCTION The properties of organic matrix composites are,in general,cure and process dependent.This may result in variations of glass transition (service temperature),corrosion stability,susceptibility to micro- cracking,general strength,or fatigue and service life.In addition,in most cases these materials or struc- tural elements constructed from them are the products of complex multi-step materials processes.Fig- ures 2.1(a)and(b)illustrate the nature of the processing pipeline from raw materials to composite end item.Each rectangle in Figure 2.1(b)represents a process during which additional variability may be in- troduced into the material.Utilization of a standard composite material property database necessitates an understanding of the dependency of the measured material properties on the characteristics and variabil- ity associated with the constituent materials and the sequence of processes used to combine these mate- rials into end products.As a result,development and application of processing controls are essential to achieve the desired mechanical and physical properties for composite structures. 2.2 PURPOSE The purpose of this chapter is to provide an understanding of the origins and nature of proc- ess-induced variability in these materials in the context of an overview of types of composite materials and the associated material processing methodologies.It also seeks to addresses various approaches to minimizing variability,including implementation of process control,and the use of materials and process- ing specifications. 2.3 SCOPE This chapter includes descriptions of composite materials from the perspective of their introduction into the material pipeline as the constituent raw material,subsequent conversion of raw materials into intermediate product forms such as prepregs,and finally the utilization of these intermediate product forms by fabricators to process the materials further to form completed composite structures.Emphasis is placed on the cumulative effects that each processing phase in the pipeline contributes to the final products general quality as well as physical,chemical,and mechanical properties.Finally it includes an overview of common process control schemes and discusses preparation of materials and processing specifications. 2.4 CONSTITUENT MATERIALS 2.4.1 Fibers 2.4.1.1 Carbon and graphite fibers Carbon and graphite have substantial capability as reinforcing fibers,with great flexibility in the prop- erties that can be provided.Primary characteristics for reinforcing fibers in polymer matrix composites are high stiffness and strength.The fibers must maintain these characteristics in hostile environments such as elevated temperatures,exposure to common solvents and fluids,and environmental moisture.To be used as part of a primary structure material it should also be available as continuous fiber(Reference 2.4.1.1). These characteristics and requirements have substantial implications for the physical,chemical and me- chanical properties of the fiber,which in turn implies processing and acceptance parameters. 2-1
MIL-HDBK-17-3F Volume 3, Chapter 2 Materials and Processes - The Effects of Variability on Composite Properties 2-1 CHAPTER 2 MATERIALS AND PROCESSES - THE EFFECTS OF VARIABILITY ON COMPOSITE PROPERTIES 2.1 INTRODUCTION The properties of organic matrix composites are, in general, cure and process dependent. This may result in variations of glass transition (service temperature), corrosion stability, susceptibility to microcracking, general strength, or fatigue and service life. In addition, in most cases these materials or structural elements constructed from them are the products of complex multi-step materials processes. Figures 2.1(a) and (b) illustrate the nature of the processing pipeline from raw materials to composite end item. Each rectangle in Figure 2.1(b) represents a process during which additional variability may be introduced into the material. Utilization of a standard composite material property database necessitates an understanding of the dependency of the measured material properties on the characteristics and variability associated with the constituent materials and the sequence of processes used to combine these materials into end products. As a result, development and application of processing controls are essential to achieve the desired mechanical and physical properties for composite structures. 2.2 PURPOSE The purpose of this chapter is to provide an understanding of the origins and nature of process-induced variability in these materials in the context of an overview of types of composite materials and the associated material processing methodologies. It also seeks to addresses various approaches to minimizing variability, including implementation of process control, and the use of materials and processing specifications. 2.3 SCOPE This chapter includes descriptions of composite materials from the perspective of their introduction into the material pipeline as the constituent raw material, subsequent conversion of raw materials into intermediate product forms such as prepregs, and finally the utilization of these intermediate product forms by fabricators to process the materials further to form completed composite structures. Emphasis is placed on the cumulative effects that each processing phase in the pipeline contributes to the final products general quality as well as physical, chemical, and mechanical properties. Finally it includes an overview of common process control schemes and discusses preparation of materials and processing specifications. 2.4 CONSTITUENT MATERIALS 2.4.1 Fibers 2.4.1.1 Carbon and graphite fibers Carbon and graphite have substantial capability as reinforcing fibers, with great flexibility in the properties that can be provided. Primary characteristics for reinforcing fibers in polymer matrix composites are high stiffness and strength. The fibers must maintain these characteristics in hostile environments such as elevated temperatures, exposure to common solvents and fluids, and environmental moisture. To be used as part of a primary structure material it should also be available as continuous fiber (Reference 2.4.1.1). These characteristics and requirements have substantial implications for the physical, chemical and mechanical properties of the fiber, which in turn implies processing and acceptance parameters
MIL-HDBK-17-3F Volume 3,Chapter 2 Materials and Processes-The Effects of Variability on Composite Properties 2.4.1.1.1 Carbon vs.graphite Interest in carbon fibers for structural materials was initiated in the late 1950s when synthesized ray- ons in textile form were carbonized to produce carbon fibers for high temperature missile applications (Reference 2.4.1.1.1).One of the first distinctions to be made is the difference between carbon and graphite fibers,although the terms are frequently used interchangeably.Background information for these differences is contained in the following sections.The primary purpose of making this distinction here is to alert the reader that users may mean different things when referring to graphite versus carbon fibers. ALL PRODUCTS,REGARDLESS TO STAGE OF WORK,ARE CONSID- ERED AS RAW MATERIALS.THESE MAY BE CHEMICALS FOR RAW RESINS,OR SAND TO PROCESS INTO GLASS PRODUCTS,OR PRECURSORS FOR FILAMENTS,OR WOVEN GOODS,OR FLAT MATERIAL PROCESSED SHEETS AND/OR MANY OTHER ARTICLES WHICH HAVE YET TO BE PROCESSED TO AN END ITEM. EACH RAW PRODUCT THEN IS PROCESSED,OR MIXED WITH OTHER RAW PRODUCTS,OR ALTERED TO BECOME STILL ANOTH- MANUFACTURE ER RAW ARTICLE TO EXPERIENCE YET ADDITIONAL PROCESS STEPS THROUGH THE PIPELINE.EACH AS RECEIVED RAW &/OR ARTICLE MUST BE PROCESSED IN SUCH A MANNER DURING ITS PROCESSING STEP(S)THAT VARIABILITY IS MINIMIZED AT THE PROCESSING NEXT PIPELINE FUNCTION.PROCESSING FUNCTIONS MAY BE COMPLEX;SUCH AS MATRIX IMPREGNATION,OR THEY MAY BE RELATIVELY SIMPLE;SUCH AS SHIPPING.REGARDLESS,EACH STEP MUST BE EFFECTIVE IN THAT IT DOES NOT INTRODUCE UNCONTROLLED CHANGES THAT ALTER THE PRODUCT FOR SUBSEQUENT USE OR END ITEM PERFORMANCE. FINISHED ARTICLES LEAVING ONE PROCESSING FUNCTION IS USUALLY STILL CONSIDERED A RAW PRODUCT WHEN DELIVERED FINISHED TO THE NEXT.THE ONUS FOR CONSISTENCY OF THIS PRODUCT MUST BE RECOGNIZED AND ATTENDED TO DURING THE JUST ARTICLE COMPLETED PROCESSING STEP(S).THE MATERIALS PIPELINE IS NOT COMPLETE UNTIL THE END ARTICLE IS FULLY FUNCTIONAL AS IS. FIGURE 2.1(a) Composite materials and processing,basic pipeline common to all materials and processes. 2-2
MIL-HDBK-17-3F Volume 3, Chapter 2 Materials and Processes - The Effects of Variability on Composite Properties 2-2 2.4.1.1.1 Carbon vs. graphite Interest in carbon fibers for structural materials was initiated in the late 1950s when synthesized rayons in textile form were carbonized to produce carbon fibers for high temperature missile applications (Reference 2.4.1.1.1). One of the first distinctions to be made is the difference between carbon and graphite fibers, although the terms are frequently used interchangeably. Background information for these differences is contained in the following sections. The primary purpose of making this distinction here is to alert the reader that users may mean different things when referring to graphite versus carbon fibers. FIGURE 2.1(a) Composite materials and processing, basic pipeline common to all materials and processes
MIL-HDBK-17-3F Volume 3,Chapter 2 Materials and Processes-The Effects of Variability on Composite Properties RAW RESIN FIBER RAW MATERIAL MANUFACTURE MANUFACTURE MATERIAL PRODUCTS PRODUCT STRAND,TOW ROVING RAW RAW RAW MATERIAL MATERIAL MATERIAL RTM WET PREPREGER WEAVER MANUFACTURERS MANUFACTURE MANUFACTURE ARTICLE FINISHED FABRIC GOODS PRODUCTS PRODUCTS PRODUCTS FIGURE 2.1(b)Raw materials pipeline (example). Carbon and graphite fibers are both based on graphene(hexagonal)layer networks present in car- bon.If the graphene layers or planes stack with three dimensional order the material is defined as graph- ite (Reference 2.4.1.1.1).Usually extended time and temperature processing is required to form this or- der,making graphite fibers more expensive.Because the bonding between planes is weak,disorder fre- quently occurs such that only the two dimensional ordering within the layers is present.This material is 2-3
MIL-HDBK-17-3F Volume 3, Chapter 2 Materials and Processes - The Effects of Variability on Composite Properties 2-3 FIGURE 2.1(b) Raw materials pipeline (example). Carbon and graphite fibers are both based on graphene (hexagonal) layer networks present in carbon. If the graphene layers or planes stack with three dimensional order the material is defined as graphite (Reference 2.4.1.1.1). Usually extended time and temperature processing is required to form this order, making graphite fibers more expensive. Because the bonding between planes is weak, disorder frequently occurs such that only the two dimensional ordering within the layers is present. This material is
MIL-HDBK-17-3F Volume 3,Chapter 2 Materials and Processes-The Effects of Variability on Composite Properties defined as carbon (Reference 2.4.1.1.1).With this distinction made,it should be understood that while some differences are implied,there is not a single condition which strictly separates carbon from graphite fibers,and even graphite fibers retain some disorder in their structure. 2.4.1.1.2 General material description Three different precursor materials are commonly used at present to produce carbon fibers:rayon, polyacrylonitrile(PAN),and isotropic and liquid crystalline pitches(Reference 2.4.1.1.1).Carbon fibers are made predominately from carbonization of PAN.The fibers consist of intermingled fibrils of turbostratic graphite with basal planes tending to align along the fiber axis.This forms an internal structure reminis- cent of an onion skin.Pitch fibers may have a different internal structure,more like sheafs or spokes(Ref- erence2.4.1.1). The highly anisotropic morphology gives rise to moduli in the range of 200-750 GPa parallel to the fiber long axis,and around 20 GPa in the normal direction.For comparison,single crystal (whisker)of graphite is about 1060 and 3 GPa,respectively,but these properties are not attainable in fiber form.Ultra high modulus fibers can be prepared from liquid-crystalline mesophase pitch;the higher degree of orien- tation in the precursor translates through to the final carbonized fiber leading to larger and more oriented graphite crystallites. 2.4.1.1.3 Processing High stiffness and strength implies strong interatomic and intermolecular bonds and few strength lim- iting flaws (Reference 2.4.1.1).Carbon fiber properties are dependent on the fiber microstructure,which is extremely process dependent,such that properties of fibers with the same precursor but different proc- essing can be dramatically different.The precursor itself can also change these properties.The process- ing may be optimized for high modulus or strength,or traded off with economics. 2.4.1.1.3.1 Manufacture The manufacturing process for carbon fiber described below is for the PAN variant,which is one of the most common.Some differences between PAN processing and the pitch and rayon precursors are then described afterwards.The manufacture of PAN based carbon fiber can be broken down into the white fiber and black fiber stages.Most manufacturers consider the details of these processes proprietary. 2.4.1.1.3.1.1 White fiber Production of PAN precursor,or white fiber,is a technology in itself.Fairly conventional fiber proc- esses are performed:polymerization,spinning,drawing,and washing.Additional drawing stages may be added in the process.Characteristics of the white fiber influence the processing and results for the black fiber processing. 2.4.1.1.3.1.2 Black fiber The black fiber process consists of several steps:oxidation(or thermosetting),pyrolysis(or carboniz- ing),surface treatment,and sizing.In the oxidation process the PAN fiber is converted to a thermoset from a thermoplastic.For this oxidation process the fiber diameter is limited by waste gas diffusion.In the pyrolysis process,which is performed under an inert atmosphere,most of the non-carbon material is ex- pelled,forming ribbons of carbon aligned with the fiber axis. In the surface treatment step the fiber may be etched in either gas or liquid phase by oxidizing agents such as chlorine,bromine,nitric acid or chlorates.This improves the wettability for the resin and encour- ages formation of a strong,durable bond.Some additional improvement through removal of surface flaws may also be realized.This process can be electrolytic.The carbon fibers are often treated with solution of unmodified epoxy resin and/or other products as a size.The sizing prevents fiber abrasion,improves han- dling,and can provide an epoxy matrix compatible surface. 2-4
MIL-HDBK-17-3F Volume 3, Chapter 2 Materials and Processes - The Effects of Variability on Composite Properties 2-4 defined as carbon (Reference 2.4.1.1.1). With this distinction made, it should be understood that while some differences are implied, there is not a single condition which strictly separates carbon from graphite fibers, and even graphite fibers retain some disorder in their structure. 2.4.1.1.2 General material description Three different precursor materials are commonly used at present to produce carbon fibers: rayon, polyacrylonitrile (PAN), and isotropic and liquid crystalline pitches (Reference 2.4.1.1.1). Carbon fibers are made predominately from carbonization of PAN. The fibers consist of intermingled fibrils of turbostratic graphite with basal planes tending to align along the fiber axis. This forms an internal structure reminiscent of an onion skin. Pitch fibers may have a different internal structure, more like sheafs or spokes (Reference 2.4.1.1). The highly anisotropic morphology gives rise to moduli in the range of 200-750 GPa parallel to the fiber long axis, and around 20 GPa in the normal direction. For comparison, single crystal (whisker) of graphite is about 1060 and 3 GPa, respectively, but these properties are not attainable in fiber form. Ultra high modulus fibers can be prepared from liquid-crystalline mesophase pitch; the higher degree of orientation in the precursor translates through to the final carbonized fiber leading to larger and more oriented graphite crystallites. 2.4.1.1.3 Processing High stiffness and strength implies strong interatomic and intermolecular bonds and few strength limiting flaws (Reference 2.4.1.1). Carbon fiber properties are dependent on the fiber microstructure, which is extremely process dependent, such that properties of fibers with the same precursor but different processing can be dramatically different. The precursor itself can also change these properties. The processing may be optimized for high modulus or strength, or traded off with economics. 2.4.1.1.3.1 Manufacture The manufacturing process for carbon fiber described below is for the PAN variant, which is one of the most common. Some differences between PAN processing and the pitch and rayon precursors are then described afterwards. The manufacture of PAN based carbon fiber can be broken down into the white fiber and black fiber stages. Most manufacturers consider the details of these processes proprietary. 2.4.1.1.3.1.1 White fiber Production of PAN precursor, or white fiber, is a technology in itself. Fairly conventional fiber processes are performed: polymerization, spinning, drawing, and washing. Additional drawing stages may be added in the process. Characteristics of the white fiber influence the processing and results for the black fiber processing. 2.4.1.1.3.1.2 Black fiber The black fiber process consists of several steps: oxidation (or thermosetting), pyrolysis (or carbonizing), surface treatment, and sizing. In the oxidation process the PAN fiber is converted to a thermoset from a thermoplastic. For this oxidation process the fiber diameter is limited by waste gas diffusion. In the pyrolysis process, which is performed under an inert atmosphere, most of the non-carbon material is expelled, forming ribbons of carbon aligned with the fiber axis. In the surface treatment step the fiber may be etched in either gas or liquid phase by oxidizing agents such as chlorine, bromine, nitric acid or chlorates. This improves the wettability for the resin and encourages formation of a strong, durable bond. Some additional improvement through removal of surface flaws may also be realized. This process can be electrolytic. The carbon fibers are often treated with solution of unmodified epoxy resin and/or other products as a size. The sizing prevents fiber abrasion, improves handling, and can provide an epoxy matrix compatible surface
MIL-HDBK-17-3F Volume 3,Chapter 2 Materials and Processes-The Effects of Variability on Composite Properties 2.4.1.1.3.1.3 Carbon fiber differences due to pitch/PAN/rayon precursors As a rule PAN precursor can provide higher strength carbon fibers,while pitch can provide higher moduli.Rayon based fibers tend to be less expensive but lower performance.Pitch fiber composites have been prepared with elastic moduli superior to steel,and electrical conductivity higher than copper conduc- tor.The shear strengths and impact resistance are degraded,however(Reference 2.4.1.1.3.1.3).Yield for PAN is approximately 50%,but for pitch can be as high as 90%. White Fiber Process PAN Acrylonitrile Spool Polymer/ PolymerizeSpinDraw Wash. Solvent Carbon/Graphite Fiber Process Pitch Melt Spin PAN ThermosetCarbonizeGraphitize Surface SizingDrying Spool (Oxidize) Treatment 250- 1500- Drawing 200-400°C Carbon/ 2500°C 3000°C Graphite Spool FIGURE 2.4.1.1.3.1.3 Carbon fiber typical process flow diagram. 2.4.1.1.3.2 Processing to microstructure Carbon fiber properties are driven by the type and extent of defects,orientation of the fiber,and the degree of crystallinity.The precursor makeup and heat treatment can affect the crystallinity and orienta- tion.The defect content can be driven by contaminants and processing.Orientation is also greatly af- fected by the drawing process which may be repeated many times in the processing of the fibers. 2.4.1.1.3.3 Microstructure to properties The strength of a brittle material is frequently controlled by presence of flaws,their number and mag- nitude.The probability of finding a flaw is volume dependent,thus a fiber with a lower volume per unit length appears stronger.Elimination of defects drives tensile strength up,and also improves thermal and electrical conductivity,and oxidation resistance.However,increasing crystallinity too far can degrade fiber strength and modulus. 2.4.1.1.3.4 Testing As with most composite material properties,the values obtained are greatly dependent on the testing performed.Determination of fiber modulus can be especially controversial.The stress/strain response can be nonlinear,so where and how measurements are taken can greatly influence the results.As a re- sult,fibers which may appear to be substantially different in the literature may have little or no difference in modulus.Reported differences may be entirely the result of test and calculation differences.Chapter 3 in Volume I can be referenced for more information of fiber test methods. 2-5
MIL-HDBK-17-3F Volume 3, Chapter 2 Materials and Processes - The Effects of Variability on Composite Properties 2-5 2.4.1.1.3.1.3 Carbon fiber differences due to pitch/PAN/rayon precursors As a rule PAN precursor can provide higher strength carbon fibers, while pitch can provide higher moduli. Rayon based fibers tend to be less expensive but lower performance. Pitch fiber composites have been prepared with elastic moduli superior to steel, and electrical conductivity higher than copper conductor. The shear strengths and impact resistance are degraded, however (Reference 2.4.1.1.3.1.3). Yield for PAN is approximately 50%, but for pitch can be as high as 90%. Thermoset (Oxidize) Drawing Carbonize Graphitize Surface Treatment PAN Sizing Drying Spool Pitch Melt Spin Carbon/ Graphite Spool Acrylonitrile Polymer/ Solvent Polymerize Spin Draw Wash PAN Spool White Fiber Process Carbon/Graphite Fiber Process 200-400°C 250- 2500°C 1500- 3000°C FIGURE 2.4.1.1.3.1.3 Carbon fiber typical process flow diagram. 2.4.1.1.3.2 Processing to microstructure Carbon fiber properties are driven by the type and extent of defects, orientation of the fiber, and the degree of crystallinity. The precursor makeup and heat treatment can affect the crystallinity and orientation. The defect content can be driven by contaminants and processing. Orientation is also greatly affected by the drawing process which may be repeated many times in the processing of the fibers. 2.4.1.1.3.3 Microstructure to properties The strength of a brittle material is frequently controlled by presence of flaws, their number and magnitude. The probability of finding a flaw is volume dependent, thus a fiber with a lower volume per unit length appears stronger. Elimination of defects drives tensile strength up, and also improves thermal and electrical conductivity, and oxidation resistance. However, increasing crystallinity too far can degrade fiber strength and modulus. 2.4.1.1.3.4 Testing As with most composite material properties, the values obtained are greatly dependent on the testing performed. Determination of fiber modulus can be especially controversial. The stress/strain response can be nonlinear, so where and how measurements are taken can greatly influence the results. As a result, fibers which may appear to be substantially different in the literature may have little or no difference in modulus. Reported differences may be entirely the result of test and calculation differences. Chapter 3 in Volume I can be referenced for more information of fiber test methods
MIL-HDBK-17-3F Volume 3,Chapter 2 Materials and Processes-The Effects of Variability on Composite Properties 2.4.1.1.4 Typical properties Typically limitations on the end use for carbon fibers in composite structure depend more on the resin matrix than the fiber.Some exceptions to this are present,however,in which case the oxidative stability, thermal conductivity,coefficient of thermal expansion,or other properties of the fiber must be taken into account.Some key properties for carbon fiber,including cost,are listed in Table 2.4.1.1.4.Typical values for glass,aramid,and boron are shown for comparison.While some carbon fiber properties are fairly uni- versal,different products from different manufacturers can have substantially different properties.Three of the major manufacturers for the US are Amoco,Hercules and Toray.It should be noted that translation of fiber properties to composite properties is dependent on many factors in addition to rule of mixtures. TABLE 2.4.1.1.4 Comparison of carbon and other fiber properties. Tensile Tensile Density, Fiber Cost.$/ Modulus. Strength,ksi g/cm Diameter, Msi micron Carbon(PAN) 30-50 350-1000 1.75-1.90 4-8 20-100 Carbon(Pitch) 25-110 200-450 1.90-2.15 8-11 40-200 Carbon(Rayon)】 6 150 1.6 8-9 5-25 Glass 10-12.5 440-670 2.48-2.62 30 5-40 Aramid 20 410 1.44 25-75 Boron 58 730-1000 2.3-2.6 100-200 100-250 2.4.1.2 Aramid In the early 1970's,Du Pont Company introduced KevlarTM aramid,an organic fiber with high specific tensile modulus and strength.This was the first organic fiber to be used as a reinforcement in advanced composites.Today this fiber is used in various structural parts including reinforced plastics,ballistics, tires,ropes,cables,asbestos replacement,coated fabrics,and protective apparel.Aramid fiber is manu- factured by extruding a polymer solution through a spinneret.Major forms available from Du Pont are continuous filament yarns,rovings,chopped fiber,pulp,spun-laced sheet,wet-laid papers,thermoplastic- impregnated tows,and thermoformable composite sheets. Important generic properties of aramid fibers are:low density,high tensile strength,high tensile stiff- ness,low compressive properties(nonlinear),and exceptional toughness characteristics.The density of aramid is 0.052 Ib/in(1.44 gm/cm).This is about 40%lower than glass and about 20%lower than com- monly used carbon.Aramids do not melt and they decompose at about 900F(500C).Tensile strength of yarn,measured in twisted configuration,can be varied from 500-600 ksi(3.4-4.1 GPa)by choosing different types of aramids.The nominal coefficient of thermal expansion is 3x105 in/in/F (-5x10 m/m/C)in the axial direction.Aramid fibers,being aromatic polyamide polymers,have high thermal stability and dielectric and chemical properties.Excellent ballistic performance and general dam- age tolerance is derived from fiber toughness.Aramid is used,in fabric or composite form,to achieve ballistic protection for humans,armored tanks,military aircraft,and so on. Composite systems,reinforced with aramid,have excellent vibration-damping characteristics.They resist shattering upon impact.Temperature of use,in composite form with polymer matrix,range from-33 to 390F(-36-200C),The nominal tensile properties of composites reinforced with aramid are listed in Table 2.4.1.2(a)-in thermoset(Reference 2.4.1.2(a))and thermoplastic (Reference 2.4.1.2(b))resin ma- trix.At 60%fiber volume fraction,composites of epoxy reinforced with aramid fibers have nominal tensile 2-6
MIL-HDBK-17-3F Volume 3, Chapter 2 Materials and Processes - The Effects of Variability on Composite Properties 2-6 2.4.1.1.4 Typical properties Typically limitations on the end use for carbon fibers in composite structure depend more on the resin matrix than the fiber. Some exceptions to this are present, however, in which case the oxidative stability, thermal conductivity, coefficient of thermal expansion, or other properties of the fiber must be taken into account. Some key properties for carbon fiber, including cost, are listed in Table 2.4.1.1.4. Typical values for glass, aramid, and boron are shown for comparison. While some carbon fiber properties are fairly universal, different products from different manufacturers can have substantially different properties. Three of the major manufacturers for the US are Amoco, Hercules and Toray. It should be noted that translation of fiber properties to composite properties is dependent on many factors in addition to rule of mixtures. TABLE 2.4.1.1.4 Comparison of carbon and other fiber properties. Tensile Modulus, Msi Tensile Strength, ksi Density, g/cm3 Fiber Diameter, micron Cost, $/# Carbon (PAN) 30-50 350-1000 1.75-1.90 4-8 20-100 Carbon (Pitch) 25-110 200-450 1.90-2.15 8-11 40-200 Carbon (Rayon) 6 150 1.6 8-9 5-25 Glass 10-12.5 440-670 2.48-2.62 30 5-40 Aramid 20 410 1.44 -- 25-75 Boron 58 730-1000 2.3-2.6 100-200 100-250 2.4.1.2 Aramid In the early 1970's, Du Pont Company introduced Kevlar™ aramid, an organic fiber with high specific tensile modulus and strength. This was the first organic fiber to be used as a reinforcement in advanced composites. Today this fiber is used in various structural parts including reinforced plastics, ballistics, tires, ropes, cables, asbestos replacement, coated fabrics, and protective apparel. Aramid fiber is manufactured by extruding a polymer solution through a spinneret. Major forms available from Du Pont are continuous filament yarns, rovings, chopped fiber, pulp, spun-laced sheet, wet-laid papers, thermoplasticimpregnated tows, and thermoformable composite sheets. Important generic properties of aramid fibers are: low density, high tensile strength, high tensile stiffness, low compressive properties (nonlinear), and exceptional toughness characteristics. The density of aramid is 0.052 lb/in3 (1.44 gm/cm3 ). This is about 40% lower than glass and about 20% lower than commonly used carbon. Aramids do not melt and they decompose at about 900°F (500°C). Tensile strength of yarn, measured in twisted configuration, can be varied from 500 - 600 ksi (3.4 - 4.1 GPa) by choosing different types of aramids. The nominal coefficient of thermal expansion is 3x10-6 in/in/F° (-5x10-6 m/m/C°) in the axial direction. Aramid fibers, being aromatic polyamide polymers, have high thermal stability and dielectric and chemical properties. Excellent ballistic performance and general damage tolerance is derived from fiber toughness. Aramid is used, in fabric or composite form, to achieve ballistic protection for humans, armored tanks, military aircraft, and so on. Composite systems, reinforced with aramid, have excellent vibration-damping characteristics. They resist shattering upon impact. Temperature of use, in composite form with polymer matrix, range from -33 to 390°F (-36 - 200°C), The nominal tensile properties of composites reinforced with aramid are listed in Table 2.4.1.2(a) - in thermoset (Reference 2.4.1.2(a)) and thermoplastic (Reference 2.4.1.2(b)) resin matrix. At 60% fiber volume fraction, composites of epoxy reinforced with aramid fibers have nominal tensile
MIL-HDBK-17-3F Volume 3,Chapter 2 Materials and Processes-The Effects of Variability on Composite Properties strength (room temperature)of 200 ksi (1.4 GPa)and nominal tensile modulus of 11 Msi (76 GPa). These composites are ductile under compression and flexure.Ultimate strength,under compression or flexure,is lower than glass or carbon composites.Composite systems,reinforced with aramid,are resis- tant to fatigue and stress rupture.In the system of epoxy reinforced with aramid,under tension/tension fatigue,unidirectional specimens (Vr~60%)survive 3,000,000 cycles at 50%of their ultimate stress (Reference 2.4.1.2(a)).Recently,thermoplastic resin composites reinforced with aramid have been de- veloped.These thermoplastic composite systems have exhibited equivalent mechanical properties com- pared to similar thermoset systems (Reference 2.4.1.2(b)).In addition,thermoplastic systems provide potential advantages in economical processing (Reference 2.4.1.2(c)),bonding,and repair.A unique thermoformable sheet product,in thermoplastic matrix reinforced with aramid fibers,is available (Refer- ence 2.4.1.2(d)).These composite systems are also used to achieve low coefficient of thermal expansion or high wear resistance.They are non-conductive and exhibit no galvanic reaction with metals.Aramid fibers are available in several forms with different fiber modulus (Table 2.4.1.2(b)).KevlarTM29 has the lowest modulus and highest toughness (strain to failure~4%).These fibers are used mostly in ballistics and other soft composite systems such as cut-and slash-resistance protective apparel,ropes,coated fabric,asbestos replacement,pneumatic tires,etc.These are also used for composites where maximum impact and damage tolerance is critical and stiffness is less important.KevlarTM49 is predominantly used in reinforced plastics-both in thermoplastic and thermoset resin systems.It is also used in soft compos- ites like core of fiber optic cable and mechanical rubber good systems(e.g.,high pressure flexible hose, radiator hose,power transmission belts,conveyor belts,etc.).An ultra-high modulus Type 149 has been made available recently.It has 40%higher modulus than KevlarTM49.KevlarTM29 is available in fiber yarn sizes and two rovings sizes.KevlarTM49 is available in six yarn and two rovings sizes.KevlarTM149 is available in three yarn sizes.Yarn sizes range from the very fine 55 denier(30 filaments)to 3000 den- ier(1300 filaments).Rovings are 4560 denier(3072 filaments)and 7100 denier(5000 filaments).Com- posite thermoplastic tows,several types of melt-impregnated thermoplastic reinforced with different Kev- larTM yarns and deniers,are also available. TABLE 2.4.1.2(a)Nominal composite properties reinforced with aramid fiber(V~60%). Thermoset (epoxy) Thermoplastic(J2) Tensile Units unidirectional fabric unidirectional fabric' Property Modulus Msi(GPa) 11(68.5) 6(41) 10.5-11.5(73-79) 5.1-5.8(35-40) Strength ksi(GPa) 200(1.4) 82(0.56) 180-200(1.2-1.4) 77-83(0.53-0.57 1 Normalized from Vr=40%;fabric style S285 Aramid composites were first adopted in applications where weight savings were critical-for exam- ple,aircraft components,helicopters,space vehicles,and missiles.Armor applications resulted from the superior ballistic and structural performance.In marine recreational industries,light weight,stiffness, vibration damping,and damage tolerance are valued.Composites reinforced with aramids are used in the hulls of canoes,kayaks,and sail and power boats.These same composite attributes have led to use in sports equipment.Composite applications of aramid continue to grow as systems are developed to capitalize on other properties.The stability and frictional properties of aramids at high temperatures have led to brake,clutch,and gasket uses;low coefficient of thermal expansion is being used in printed wiring boards;and exceptional wear resistance is being engineered into injection-molded thermoplastic indus- trial parts.Melt-impregnated thermoplastic composites,reinforced with aramids,offer unique processing advantages-e.g.,in-situ consolidation of filament-wound parts.These can be used for manufacturing thick parts where processing is otherwise very difficult(Reference 2.4.1.2(e)). 2-7
MIL-HDBK-17-3F Volume 3, Chapter 2 Materials and Processes - The Effects of Variability on Composite Properties 2-7 strength (room temperature) of 200 ksi (1.4 GPa) and nominal tensile modulus of 11 Msi (76 GPa). These composites are ductile under compression and flexure. Ultimate strength, under compression or flexure, is lower than glass or carbon composites. Composite systems, reinforced with aramid, are resistant to fatigue and stress rupture. In the system of epoxy reinforced with aramid, under tension/tension fatigue, unidirectional specimens (Vf ~ 60%) survive 3,000,000 cycles at 50% of their ultimate stress (Reference 2.4.1.2(a)). Recently, thermoplastic resin composites reinforced with aramid have been developed. These thermoplastic composite systems have exhibited equivalent mechanical properties compared to similar thermoset systems (Reference 2.4.1.2(b)). In addition, thermoplastic systems provide potential advantages in economical processing (Reference 2.4.1.2(c)), bonding, and repair. A unique thermoformable sheet product, in thermoplastic matrix reinforced with aramid fibers, is available (Reference 2.4.1.2(d)). These composite systems are also used to achieve low coefficient of thermal expansion or high wear resistance. They are non-conductive and exhibit no galvanic reaction with metals. Aramid fibers are available in several forms with different fiber modulus (Table 2.4.1.2(b)). Kevlar™29 has the lowest modulus and highest toughness (strain to failure ~ 4%). These fibers are used mostly in ballistics and other soft composite systems such as cut- and slash- resistance protective apparel, ropes, coated fabric, asbestos replacement, pneumatic tires, etc. These are also used for composites where maximum impact and damage tolerance is critical and stiffness is less important. Kevlar™49 is predominantly used in reinforced plastics - both in thermoplastic and thermoset resin systems. It is also used in soft composites like core of fiber optic cable and mechanical rubber good systems (e.g., high pressure flexible hose, radiator hose, power transmission belts, conveyor belts, etc.). An ultra-high modulus Type 149 has been made available recently. It has 40% higher modulus than Kevlar™49. Kevlar™29 is available in fiber yarn sizes and two rovings sizes. Kevlar™49 is available in six yarn and two rovings sizes. Kevlar™149 is available in three yarn sizes. Yarn sizes range from the very fine 55 denier (30 filaments) to 3000 denier (1300 filaments). Rovings are 4560 denier (3072 filaments) and 7100 denier (5000 filaments). Composite thermoplastic tows, several types of melt-impregnated thermoplastic reinforced with different Kevlar™ yarns and deniers, are also available. TABLE 2.4.1.2(a) Nominal composite properties reinforced with aramid fiber (Vf ~ 60%). Thermoset (epoxy) Thermoplastic (J2) Tensile Property Units unidirectional fabric1 unidirectional fabric1 Modulus Msi (GPa) 11 (68.5) 6 (41) 10.5-11.5 (73-79) 5.1-5.8 (35-40) Strength ksi (GPa) 200 (1.4) 82 (0.56) 180-200 (1.2-1.4) 77-83 (0.53-0.57) 1 Normalized from Vf = 40%; fabric style S285 Aramid composites were first adopted in applications where weight savings were critical - for example, aircraft components, helicopters, space vehicles, and missiles. Armor applications resulted from the superior ballistic and structural performance. In marine recreational industries, light weight, stiffness, vibration damping, and damage tolerance are valued. Composites reinforced with aramids are used in the hulls of canoes, kayaks, and sail and power boats. These same composite attributes have led to use in sports equipment. Composite applications of aramid continue to grow as systems are developed to capitalize on other properties. The stability and frictional properties of aramids at high temperatures have led to brake, clutch, and gasket uses; low coefficient of thermal expansion is being used in printed wiring boards; and exceptional wear resistance is being engineered into injection-molded thermoplastic industrial parts. Melt-impregnated thermoplastic composites, reinforced with aramids, offer unique processing advantages - e.g., in-situ consolidation of filament-wound parts. These can be used for manufacturing thick parts where processing is otherwise very difficult (Reference 2.4.1.2(e))
MIL-HDBK-17-3F Volume 3,Chapter 2 Materials and Processes-The Effects of Variability on Composite Properties TABLE 2.4.1.2(b)Nominal properties of aramid fiber. Tensile Property Units Type of Kevlar TM 29 49 149 Modulus Msi(GPa) 12(83) 18(124) 25(173) Strength ksi(GPa) 525(3.6) 525-600(3.6-4.1) 500(3.4) Aramid fiber is relatively flexible and tough.Thus it can be combined with resins and processed into composites by most of the methods established for glass.Yarns and rovings are used in filament wind- ing,prepreg tape,and in pultrusion.Woven fabric prepreg is the major form used in thermoset compos- ites.Aramid fiber is available in various weights,weave patterns,and constructions;from very thin (0.0002 in.,0.005mm)lightweight(275 gm/m2)to thick(0.026 in.,0.66 mm)heavy (2.8 gm/m)woven roving.Thermoplastic-impregnated tows can be woven into various types of fabrics to form prepregs. These composites demonstrate good property retention under hot and humid conditions (Reference 2.4.1.2(f)).Chopped aramid fiber is available in lengths from 6 mm to 100 mm.The shorter lengths are used to reinforce thermoset,thermoplastic,and elastomeric resins in automotive brake and clutch linings, gaskets,and electrical parts.Needle-punched felts and spun yarns for asbestos replacement applica- tions are made from longer fiber staple.A unique very short fiber(0.08-0.16 in.,2-4 mm)with many attached fibrils is available(aramid pulp).It can provide efficient reinforcement in asbestos replacement uses.Aramid short fibers can be processed into spun-laced and wet-laid papers.These are useful for surfacing veil,thin-printed wiring boards,and gasket material.Uniform dispersion of aramid short fiber in resin formulations is achieved through special mixing methods and equipment.Inherent fiber toughness necessitates special types of tools for cutting fabrics and machining aramid composites. 2.4.1.3 Glass Glass in the forms used in commerce has been produced by many cultures since the early Etruscan civilization.Glass as a structural material was introduced early in the seventeenth century and became widely used during the twentieth century as the technology for flat pane was perfected.Glass fibrous us- age for reinforcement was pioneered in replacement of metals and used for both commercial and military uses with the advent of formulation control and molten material which is die or bushing pulled into con- tinuous filaments.These events lead to a wide range of aerospace and commercial high performance structural applications still in use today. 2.4.1.3.1 Chemical description Glass is derived from one of our most abundant natural resources--sand.Other than for,possibly, transport and the melting process,it is not petro-chemical dependent.For purposes of this handbook the typical glass compositions are for electrical/Grade"E"glass,a calcium aluminoborosilica composition with an alkali content of less than 2%,chemical resistant "C"glass composed of soda-lime-borsilicates and high strength S-2 glass which is a low-alkali magnesi-alumina-silicate composition(See Table 2.4.1.3.1). Surface treatments(binders/sizing)can be applied directly to the filaments during the pulling step.Or- ganic binders,such as starch oil,are applied to provide optimum weaving and strand protection during weaving of fabrics or"greige goods".These type binders are then washed and heat cleaned off the fab- rics for finishing or sizing at the weaver with coupling agents to improve compatibility with resins.(See 2-8
MIL-HDBK-17-3F Volume 3, Chapter 2 Materials and Processes - The Effects of Variability on Composite Properties 2-8 TABLE 2.4.1.2(b) Nominal properties of aramid fiber. Tensile Property Units Type of Kevlar™ 29 49 149 Modulus Msi (GPa) 12 (83) 18 (124) 25 (173) Strength ksi (GPa) 525 (3.6) 525-600 (3.6-4.1) 500 (3.4) Aramid fiber is relatively flexible and tough. Thus it can be combined with resins and processed into composites by most of the methods established for glass. Yarns and rovings are used in filament winding, prepreg tape, and in pultrusion. Woven fabric prepreg is the major form used in thermoset composites. Aramid fiber is available in various weights, weave patterns, and constructions; from very thin (0.0002 in., 0.005mm) lightweight (275 gm/m2 ) to thick (0.026 in., 0.66 mm) heavy (2.8 gm/m2 ) woven roving. Thermoplastic-impregnated tows can be woven into various types of fabrics to form prepregs. These composites demonstrate good property retention under hot and humid conditions (Reference 2.4.1.2(f)). Chopped aramid fiber is available in lengths from 6 mm to 100 mm. The shorter lengths are used to reinforce thermoset, thermoplastic, and elastomeric resins in automotive brake and clutch linings, gaskets, and electrical parts. Needle-punched felts and spun yarns for asbestos replacement applications are made from longer fiber staple. A unique very short fiber (0.08 - 0.16 in., 2 - 4 mm) with many attached fibrils is available (aramid pulp). It can provide efficient reinforcement in asbestos replacement uses. Aramid short fibers can be processed into spun-laced and wet-laid papers. These are useful for surfacing veil, thin-printed wiring boards, and gasket material. Uniform dispersion of aramid short fiber in resin formulations is achieved through special mixing methods and equipment. Inherent fiber toughness necessitates special types of tools for cutting fabrics and machining aramid composites. 2.4.1.3 Glass Glass in the forms used in commerce has been produced by many cultures since the early Etruscan civilization. Glass as a structural material was introduced early in the seventeenth century and became widely used during the twentieth century as the technology for flat pane was perfected. Glass fibrous usage for reinforcement was pioneered in replacement of metals and used for both commercial and military uses with the advent of formulation control and molten material which is die or bushing pulled into continuous filaments. These events lead to a wide range of aerospace and commercial high performance structural applications still in use today. 2.4.1.3.1 Chemical description Glass is derived from one of our most abundant natural resources--sand. Other than for, possibly, transport and the melting process, it is not petro-chemical dependent. For purposes of this handbook the typical glass compositions are for electrical/Grade "E" glass, a calcium aluminoborosilica composition with an alkali content of less than 2%, chemical resistant "C" glass composed of soda-lime-borsilicates and high strength S-2 glass which is a low-alkali magnesi-alumina-silicate composition (See Table 2.4.1.3.1). Surface treatments (binders/sizing) can be applied directly to the filaments during the pulling step. Organic binders, such as starch oil, are applied to provide optimum weaving and strand protection during weaving of fabrics or "greige goods". These type binders are then washed and heat cleaned off the fabrics for finishing or sizing at the weaver with coupling agents to improve compatibility with resins. (See
MIL-HDBK-17-3F Volume 3,Chapter 2 Materials and Processes-The Effects of Variability on Composite Properties Figure 2.4.1.3.1)The exception to this process for fabrics is when they are heat treated or"caramelized", which converts the starch to carbon(0.2-0.5%).Glass roving products (untwisted)type yarns are most often directly finished with the final coupling agents during the filament manufacturing step.Therefore the products will be identified with the glass manufacturer's product codes and the desizing step is not necessary as common with fabric"greige goods"forms.Heat cleaned products are also available where the product is essentially pure glass.These products,which are subject to damage,are commonly util- ized for silicone laminates.Another finish designation is applicable to the heat cleaned product when it is followed with a demineralized water wash(neutral pH).More common for structural applications are the coupling agents which are applied for use with standard organic polymers.During the 1940's Volan'fin- ishes were introduced.Since then,many variations/improvements identified with various company desig- nations have appeared.Perhaps the most recognized is Volan A.This finish provides good wet and dry strength properties in use with polyester,epoxy,and phenolic resins.Prior to the application of this finish the clean(ed)glass is saturated with methacrylate chromic chloride so that the chrome content of the fin- ish is between 0.03%and 0.06%.This addition enhances wet-out of the resin during cure.Perhaps more typically called out for use,but not limited to,with epoxy are the silane finishes.Most all are formulated to enhance laminate wet-out.Some also produce high laminate clarity or good composite properties in aqueous environments.Others improve high-pressure laminating,or resist adverse environment or chemical exposures.Although other finishes are used in combination with matrix materials other than epoxy,finishes may have proprietary formulations or varied designations relative to the particular glass manufacturer or weaver,it is believed the compositions are readily available to the resin compounders (prepreggers)to determine compatibility and end use purposes.Note that,non-compatible finishes are purposely applied for ornament applications. 2.4.1.3.2 Physical forms available Due to the high quantity of commercial applications for glass products,there are many product forms available.For purposes of this publication glass forms will be limited to continuous filament product forms.These forms fall into four major categories.They are continuous rovings,yarn for fabrics or braid- ing.mats,and chopped strand.(See Figure 2.4.1.3.2 and ASTM Specification D 579,Reference 2.4.1.3.2(a)for information on glass fabrics.Further discussion of fabrics may be found in Section 2.5.1 on fabrics and preforms.)They are available with a variety of physical surface treatments and finishes Most structural applications utilize fabric,roving,or rovings converted to unidirectional tapes.Perhaps the most versatile fiber type to produce glass product forms is "E"glass."E"glass is identified as such for electrical applications.This type or grade of glass has eight or more standardized filament diameters available.These range from 1.4 to 5.1 mils(3.5 to 13 micrometers).(See Table I,ASTM Specification D 578,Reference 2.4.1.3.2(b).)This facilitates very thin product forms.The "S"glasses are identified as such to signify high strength.The S-2 type glasses are available with but one filament diameter.This does not limit the availability of basic structural fabric styles for S-2 glass however.Although there are more "E"roving products,as to yields,available,this has not noticeably restricted the use of S-2 type rov- ing products or roving for unidirectional tape.S-2 type rovings are available in yields of 250,750,and 1250 yards per lb(500,1500,and 2500 m/kg).Although woven rovings may be considered a fabric product form it should be noted for its importance for military applications.Also,there are glass product forms which could be considered as complimentary products for advanced structures.These would in- clude milled fibers and chopped strand. E.I.Du Pont de Nemours 2-9
MIL-HDBK-17-3F Volume 3, Chapter 2 Materials and Processes - The Effects of Variability on Composite Properties 2-9 Figure 2.4.1.3.1) The exception to this process for fabrics is when they are heat treated or "caramelized", which converts the starch to carbon (0.2 - 0.5%). Glass roving products (untwisted) type yarns are most often directly finished with the final coupling agents during the filament manufacturing step. Therefore, the products will be identified with the glass manufacturer's product codes and the desizing step is not necessary as common with fabric "greige goods" forms. Heat cleaned products are also available where the product is essentially pure glass. These products, which are subject to damage, are commonly utilized for silicone laminates. Another finish designation is applicable to the heat cleaned product when it is followed with a demineralized water wash (neutral pH). More common for structural applications are the coupling agents which are applied for use with standard organic polymers. During the 1940's Volan1 finishes were introduced. Since then, many variations/improvements identified with various company designations have appeared. Perhaps the most recognized is Volan A. This finish provides good wet and dry strength properties in use with polyester, epoxy, and phenolic resins. Prior to the application of this finish the clean(ed) glass is saturated with methacrylate chromic chloride so that the chrome content of the finish is between 0.03% and 0.06%. This addition enhances wet-out of the resin during cure. Perhaps more typically called out for use, but not limited to, with epoxy are the silane finishes. Most all are formulated to enhance laminate wet-out. Some also produce high laminate clarity or good composite properties in aqueous environments. Others improve high-pressure laminating, or resist adverse environment or chemical exposures. Although other finishes are used in combination with matrix materials other than epoxy, finishes may have proprietary formulations or varied designations relative to the particular glass manufacturer or weaver, it is believed the compositions are readily available to the resin compounders (prepreggers) to determine compatibility and end use purposes. Note that, non-compatible finishes are purposely applied for ornament applications. 2.4.1.3.2 Physical forms available Due to the high quantity of commercial applications for glass products, there are many product forms available. For purposes of this publication glass forms will be limited to continuous filament product forms. These forms fall into four major categories. They are continuous rovings, yarn for fabrics or braiding, mats, and chopped strand. (See Figure 2.4.1.3.2 and ASTM Specification D 579, Reference 2.4.1.3.2(a) for information on glass fabrics. Further discussion of fabrics may be found in Section 2.5.1 on fabrics and preforms.) They are available with a variety of physical surface treatments and finishes. Most structural applications utilize fabric, roving, or rovings converted to unidirectional tapes. Perhaps the most versatile fiber type to produce glass product forms is "E" glass. "E" glass is identified as such for electrical applications. This type or grade of glass has eight or more standardized filament diameters available. These range from 1.4 to 5.1 mils (3.5 to 13 micrometers). (See Table I, ASTM Specification D 578, Reference 2.4.1.3.2(b).) This facilitates very thin product forms. The "S" glasses are identified as such to signify high strength. The S-2 type glasses are available with but one filament diameter. This does not limit the availability of basic structural fabric styles for S-2 glass however. Although there are more "E" roving products, as to yields, available, this has not noticeably restricted the use of S-2 type roving products or roving for unidirectional tape. S-2 type rovings are available in yields of 250, 750, and 1250 yards per lb (500, 1500, and 2500 m/kg). Although woven rovings may be considered a fabric product form it should be noted for its importance for military applications. Also, there are glass product forms which could be considered as complimentary products for advanced structures. These would include milled fibers and chopped strand. 1 E. I. Du Pont de Nemours
MIL-HDBK-17-3F Volume 3,Chapter 2 Materials and Processes-The Effects of Variability on Composite Properties TABLE 2.4.1.3.1 Typical chemical compositions of glass fiber. %(wt) E-Glass S-2 Glass HR Glass(B) (Nominals) Silicon Dioxide(SiO2) 52-56(A) 65 63.5-65.0 Aluminum Oxide(Al2O3) 12-16(A) 25 24.0-25.5 Boron Oxide(B2O3) 5-10(A) Calcium Oxide(CaO) 16-25(A) <0.5 Magnesium Oxide(MgO) 0-5(A) 10 9.5-10.5 Lithium Oxide(Li2O) Potassium Oxide(K2O) 0.c 0.0-0.2 Sodium Oxide(Na2O) 0.c. 0-2 Titanium Oxide (TiO2) O.C. 0-1.5 Cerium Oxide(CeO2) Zirconium Oxide (Zr2O2) Beryllium Oxide(BeO) Iron Oxide(Fe2O3) 0.c 0.0-0.8 Fluorine(F2) 0.c 0.0-0.1 Sulfate (SO2) Alkaline Oxides PPG 0.5-1.5 Calcium Fluoride(CAF) PPG 0.0-0.8 Finishes/Binders 0.5/3.0 2-10
MIL-HDBK-17-3F Volume 3, Chapter 2 Materials and Processes - The Effects of Variability on Composite Properties 2-10 TABLE 2.4.1.3.1 Typical chemical compositions of glass fiber. %(wt) E-Glass S-2 Glass (Nominals) HR Glass (B) Silicon Dioxide (SiO2) 52-56 (A) 65 63.5 - 65.0 Aluminum Oxide (Al2O3) 12-16 (A) 25 24.0 - 25.5 Boron Oxide (B2O3) 5-10 (A) Calcium Oxide (CaO) 16-25 (A) <0.5 Magnesium Oxide (MgO) 0-5 (A) 10 9.5 - 10.5 Lithium Oxide (Li2O) Potassium Oxide (K2O) O.C. 0.0-0.2 Sodium Oxide (Na2O) O.C. 0-2 Titanium Oxide (TiO2) O.C. 0-1.5 Cerium Oxide (CeO2) Zirconium Oxide (Zr2O2) Beryllium Oxide (BeO) Iron Oxide (Fe2O3) O.C. 0.0-0.8 Fluorine (F2) O.C. 0.0-0.1 Sulfate (SO2) Alkaline Oxides PPG 0.5-1.5 Calcium Fluoride (CAF) PPG 0.0-0.8 Finishes/Binders 0.5/3.0