Composite Materials Ahmed W Moustafa Lecture 1 Composite

Composite Materials Ahmed W. Moustafa Lecture (1)

Composite Material Two inherently different materials that when combined together produce a material with properties that exceed the constituent materials.

Composite Material Defined A materials system composed of two or more physically distinct phases whose combination produces aggregate properties that are different from those of its constituents

Composite Material Defined Examples: – – Cemented carbides (WC with Co binder) Plastic molding compounds containing fillers Rubber mixed with carbon black Wood (a natural composite as distinguished from a synthesized composite)

Why Composites are Important n n n Composites can be very strong and stiff, yet very light in weight, so ratios of strength‑to‑weight and stiffness‑to‑weight are several times greater than steel or aluminum Fatigue properties are generally better than for common engineering metals Toughness is often greater too Composites can be designed that do not corrode like steel Possible to achieve combinations of properties not attainable with metals, ceramics, or polymers alone

Disadvantages and Limitations n n Properties of many important composites are anisotropic ‑ the properties differ depending on the direction in which they are measured – this may be an advantage or a disadvantage Many of the polymer‑based composites are subject to attack by chemicals or solvents, just as the polymers themselves are susceptible to attack Composite materials are generally expensive Manufacturing methods for shaping composite materials are often slow and costly

Classification of Composite Materials 1. Traditional composites – composite materials that occur in nature or have been produced by civilizations for many years – 2. Examples: wood, concrete, asphalt Synthetic composites - modern material systems normally associated with the manufacturing industries, in which the components are first produced separately and then combined in a controlled way to achieve the desired structure, properties, and part geometry

Components in a Composite Material n Nearly all composite materials consist of two phases: 1. Primary phase - forms the matrix within which the secondary phase is imbedded 2. Secondary phase - imbedded phase sometimes referred to as a reinforcing agent, because it usually serves to strengthen the composite n The reinforcing phase may be in the form of fibers, particles, or various other geometries

Functions of the Matrix Material (Primary Phase) n n n Provides the bulk form of the part or product made of the composite material Holds the imbedded phase in place, usually enclosing and often concealing it When a load is applied, the matrix shares the load with the secondary phase, in some cases deforming so that the stress is essentially born by the reinforcing agent

Composites Offer n n n High Strength Light Weight Design Flexibility Consolidation of Parts Net Shape Manufacturing

Fiber Reinforced Polymer Matrix • Transfer Load to Reinforcement • Temperature Resistance • Chemical Resistance Reinforcement • Tensile Properties • Stiffness • Impact Resistance

Design Objective n. Performance: Strength, Temperature, Stiffness n. Manufacturing Techniques n. Life Cycle Considerations n. Cost

Matrix Considerations n End Use Temperature n. Toughness n. Cosmetic Issues n. Flame Retardant n. Processing Method n. Adhesion Requirements

Matrix Types Polyesters have good mechanical properties, electrical properties and chemical resistance. Polyesters are amenable to multiple fabrication techniques and are low cost. Vinyl Esters are similar to polyester in performance. Vinyl esters have increased resistance to corrosive environments as well as a high degree of moisture resistance.

Matrix Types Epoxy Epoxies have improved strength and stiffness properties over polyesters. Epoxies offer excellent corrosion resistance and resistance to solvents and alkalis. Cure cycles are usually longer than polyesters, however no by-products are produced. Flexibility and improved performance is also achieved by the utilization of additives and fillers.

Reinforcement Fiber Type n. Fiberglass n. Carbon n. Aramid Textile Structure n. Unidirectional n. Woven n. Braid

Fiberglass E-glass: S-2 glass: Alumina-calcium-borosilicate glass (electrical applications) Magnesuim aluminosilicate glass (reinforcements) Glass offers good mechanical, electrical, and thermal properties at a relatively low cost. Density Tensile Strength Tensile Modulus Elongation E-glass 2. 56 g/cc 390 ksi 10. 5 msi 4. 8% S-2 glass 2. 46 g/cc 620 ksi 13 msi 5. 3%

Aramid Kevlar™ & Twaron™ Para aramid fiber characterized by high tensile strength and modulus Excellent Impact Resistance Good Temperature Resistance Density Tensile Strength Tensile Modulus Elongation 1. 44 g/cc 400 ksi 18 Msi 2. 5%

Carbon Fiber PAN: Fiber made from Polyacrylonitrile precursor fiber High strength and stiffness Large variety of fiber types available Density Tensile Strength Tensile Modulus Elongation Standard Modulus Intermediate Modulus 1. 79 g/cc 600 ksi 33 Msi 1. 8 % 1. 79 g/cc 800 ksi 42 Msi 1. 8 %

Weight Considerations Aramid fibers are the lightest 1. 3 -1. 4 g/cc Carbon 1. 79 g/c Fiberglass is the heaviest 2. 4 g/cc

Strength Considerations Carbon is the strongest 600 -800 ksi Fiberglass 400 -600 ksi Aramids 400 ksi

Impact Resistance Kevlar is the toughest Fiberglass Carbon

Stiffness Considerations Carbon is the stiffest 30 -40 msi Aramids 14 msi Fiberglass 10 -13 msi

Cost Considerations Fiberglass is cost effective $5. 00 -8. 00/lb. Aramids $20. 00/lb Carbon $30. 00 -$50. 00/lb

Fabric Structures Woven: Series of Interlaced yarns at 90° to each other Knit: Series of Interlooped Yarns Braided: Series of Intertwined, Spiral Yarns Nonwoven: Oriented fibers either mechanically, chemically, or thermally bonded

Woven Fabrics Basic woven fabrics consists of two systems of yarns interlaced at right angles to create a single layer with isotropic or biaxial properties.

Physical Properties n. Construction (ends & picks) n. Weight n. Thickness n. Weave Type

Components of a Woven Fabric

Basic Weave Types Plain Weave

Basic Weave Types Satin 5 HS

Basic Weave Types 2 x 2 Twill

Basic Weave Types Non-Crimp

Braiding A braid consists of two sets of yarns, which are helically intertwined. The resulting structure is oriented to the longitudinal axis of the braid. This structure is imparted with a high level of conformability, relative low cost and ease of manufacture.

Braid Structure

Types of Braids

Triaxial Yarns • A system of longitudinal yarns can be introduced which are held in place by the braiding yarns • These yarns will add dimensional stability, improve tensile properties, stiffness and compressive strength. • Yarns can also be added to the core of the braid to form a solid braid.

Conclusions Composite materials offer endless design options. Matrix, Fiber and Preform selections are critical in the design process. Structures can be produced with specific properties to meet end use requirements.