MLZ 509 İLERİ KOMPOZİT MALZEMELER

TAYFUN KOÇAKANADOLU ÜNİVERSİTESİ MALZEME BİLİMİ VE MÜHENDİSLİĞİ

TOUGHENING MECHANISMS OF CARBON FIBER REINFORCED POLIMERIC

COMPOSITES

WHAT IS COMPOSITE? Composite materials (also called composition materials or shortened to composites) are 

materials made from two or more constituent materials with significantly different physical or chemical properties, that when combined, produce a material with characteristics different from the individual components. The new material may be preferred for many reasons: common examples include materials which are stronger, lighter or less expensive when compared to traditional materials.

Aircraft engineers are increasingly searching for structural materials that have low densities, are strong, stiff, and abrasion and impact resistant, and are not easily corroded. This is a rather formidable combination of characteristics. Frequently, strong materials are relatively dense; also, increasing the strength or stiffness generally results in a decrease in impact strength.

WHAT IS CFRcomposite Carbon is a high-performance fiber material that is the

most commonly used reinforcement in advanced (i.e., nonfiberglass) polymer-matrix composites. The reasons for this are as follows:

1. Carbon fibers have the highest specific modulus and specific strength of all reinforcing fiber materials.

2. They retain their high-tensile modulus and high strength at elevated temperatures; high-temperature oxidation, however, may be a problem.

3. At room temperature carbon fibers are not affected by moisture or a wide variety of solvents, acids, and bases.

4. These fibers exhibit a diversity of physical and mechanical characteristics, allowing composites incorporating these fibers to have specific engineered properties.

5. Fiber and composite manufacturing processes have been developed that are relatively inexpensive and cost effective.

PRODUCTION OF CFRC.

Carbon Fibers are a new breed of high-strenght materials. Carbon fibers has been described as a containing at least 90% carbon obtained by the controlled pyrolysis of appropriate fibers.

Oxidized PAN(Polyacrylonitrile) fibers. PAN fibers are the chemical precursor of high-quality carbon fiber. PAN is first thermally oxidized in air at 230 degrees to form an oxidized PAN fiber and then carbonized above 1000 degrees in inert atmosphere to make carbon fibers.

REASONS OF POPULARITY OF CARBON FIBERS IN AEROSPACE

•Carbon fiber is dominated in the aerospace industry due to the following reasons •Weight saving; 7 times as strong as most metals specific strength and 5 times as strong as most

metals tensile strength. •Low expansion and contraction over a wide range of temperatures, •High resistance to fatigue than steel and aluminum. •Better structure and offer a significant gain in fuel economy. •Reduce overhaul and maintenance cost as metals are said to be more prone to cracks and

corrosion in service.

FIBER &MATRIS UYUMU

Ara yüzey özellikleri, iki bileşenin kimyasal/morfolojik doğası ve fiziksel/termodinamik uyumuna bağlıdır ve bulk kompozitin genel performansını etkiler.

Tutunma mekanik etkileşim, adsorpsiyon ve ıslanma, elektrostatik çekim, kimyasal bağ, reaksiyon bağı ve takas reaksiyonu bağı gibi mekanizmalara bağlıdır. Temel mekanizmaların yan ısıra, hidrojen bağı, van der Waals kuvvetleri ve diğer düşük enerjili kuvvetler de göz önüne alınabilir.

MECHANISMS The composite will carry increasing loads after the first cracking of the

matrix if the pull-out resistance of the fibers at the first crack is greater than the load at first cracking;

At the cracked section, the matrix does not resist any tension and the fibers carry the entire load taken by the composite.

With an increasing load on the composite, the fibers will tend to transfer the additional stress to the matrix through bond stresses. This process of multiple cracking will continue until either fibers fail or the accumulated local debonding will lead to fiber pull-out .

During the 1970s, experimental work to find alternative raw

materials led to the introduction of carbon fibers made from a

petroleum pitch derived from oil processing. These fibers

contained about 85% carbon and had excellent flexural strength.

OPTIMIZATION PROCESS

From a material and structural point of view, there is a delicate balance in optimizing the bond between the fiber and the matrix.

If the fibers have a weak bond with the matrix, they can slip out at low loads and do not contribute very much to bridge the cracks. In this situation, the fibers do not increase the toughness of the system.

If the bond with the matrix is too strong, many of the fibers may break before they dissipate energy by sliding out. In this case, the fibers behave as non-active inclusions leading to only marginal improvement in the mechanical properties.

Arayüz artırma işlemleri: Many surface treatments of fibers have attempted to solve this problem,

including plasma spraying, chemical, flame, and radiation treatments.

Role of Fiber Size To bridge the large number of microcracks in the composite under load

and to avoid large strain localization it is necessary to have a large number of short fibers. The uniform distribution of short fibers can increase the strength and ductility of the composite.

Long fibers are needed to bridge discrete macrocracks at higher loads; however the volume fraction of long fibers can be much smaller than the volume fraction of short fibers. The presence of long fibers significantly reduces the workability of the mix.

THE EFFECT OF FIBER REINFORCEMENT ON THE FRACTURE TOUGHNESS AND FLEXURAL

STRENGTH 1. The use of fibers is an effective method to increase the fracture

toughness and flexural strength of provisional restoration resin. 2. The surface treatment of the fibers greatly influences their effect on the

fracture toughness and flexural strength of provisional restoration resin.

When plasma-treated polyethylene fibers were used, a significant increase in strength was shown. Silanized glass fibers are promising new materials because of their good adhesion(yapışma) to the polymer matrix, high esthetic quality, and the increased strength of the resulting composite. Others have found that the position, quantity, and direction of the fibers and the degree of adhesion between the fibers and the polymer affect the degree of reinforcement.

SILANIZATION(ISLANABİLİRLİK)

Silanization is the covering of a surface through self-assembly with organofunctional alkoxysilane molecules. Mineral componentslike Mica, glass and metal oxide surfaces can all be silanized, because they contain hydroxyl groups which attack and displace the alkoxy groups on the silane thus forming a covalent -Si-O-Si- bond. The goal of silanization is to form bonds across the interface between mineral components and organic components present in paints, adhesives, etc. Silanization (or siliconization) of glassware increases its hydrophobicity and is used in cell culturing to reduce adherence of cells to flask walls.

TEST PREPARATION

Researchers, believe that fracture toughness is the best mechanical property measured to predict the wear and the fracture resistance of a restorative material.

Compact test specimens were fabricated following ASTM no. E 399-83 recommendations, with the dimensions and shape shown in Figure 1.

Damage Detection And Characterization

Composite defects or damage come from manufacturing or service exposure. Defects and handling damages that occur during manufacturing are controlled by in-process and post process QCs. (NDT)

COMPARISON OF COST VE MECHANICAL PROPERTIES

DEFECT LEVELS OF CFRC.

FUTURE EXPECTATIONS